Alternator Diode Test With Multimeter
Connect the positive lead of multimeter to cathode of the diode and negative lead to anode of the diode. Next set the meter to AC Volts. The best way to identify alternator problems is by conducting a bench test. 4L equipped car, pick up or SUV, is a simple test that can be done with just a multimeter. The AC ripple will cause havoc on the electronic brain. Alternator Testing. now switch everything electrical on (demister, lights, radio etc. If you don’t have a multi-meter then a bulb test is very good, often a bit more instructive. If the AO (alternator output) is disconnected when charging, sometimes it fries diodes. The best way to test is to actually disassemble the alternator, take the rectifier out and test each diode with the diode test on the multimeter. 8 volts (14. I used the multimeter to find what fuses shut off when the car did and what stayed on so I could connect the cam accordingly. What is the best way to test a 3 prong Diode to see if it is working. This type of test equipment is a good investment for a repair shop, however an alternator can be checked with the use of a reasonably priced volt-ohm (VOM) meter. A bench test will check the diodes and internal regulator and then tell you if the alternator is capable of producing its rated current and voltage. Alternator Output Test. Replacing Diodes and Brushes in a Denso Alternator Remove the 10mm nut at the B+ post, the three 8mm nuts and the 8mm head screw. This means having to replace the. All of these are a recipe for battery disaster and can potentially leave you stranded. Reverse the meter leads and note the meter reading. 1) Remove sensing diode block from the alternator before making tests. Home > Auto Meter. Remove the Diodes and measure it with an Ohm Meter or Diode tester. Re: 10si alternator ? i dont have a way to check the amps but i do have a test light and a volt meter. That test indicated it could be a bad diode that was slowly draining the battery when the car was off, hence why if it sits for more then a day its basically dead. Switch selector to diode/stator test, switch on headlamps to load generator. The Charging System Electrical Circuit Diagnosis - Course 623 5-7 Current in the charging system changes for these three different operating conditions: •Ignition switch to ON - engine stopped •Ignition switch to ON - engine running alternator output below desired voltage •Ignition switch to ON - engine running alternator output above. The bridge is located in and fastened to the alternator case. I guess a diode is stopping the test current the other direction. 917272280 Craftsman lawn tractor. Alternator Testing. With the engine at idle, multimeter monitoring the battery voltage, wiggle the engine harness starting from the battery area all the way to the ECU and see if you could duplicate the concern. If you are having problems with the charging system, you may need to test the rectifier for functionality. Connect wires one at a time to see what lead is drawing current. You can use an AC voltmeter to check for leakages. Reverse the test leads) and note the measurement. Performing a routine voltage drop test between the alternator and the battery is the best insurance against repeated trio failure. Be sure it has a diode test function if you need to go out and buy one). Peakmeter Pm2008a 2000 Counts Lcd Display Digital Clamp Multimeter Continuity Diode Testing With Auto / Manual Range , Find Complete Details about Peakmeter Pm2008a 2000 Counts Lcd Display Digital Clamp Multimeter Continuity Diode Testing With Auto / Manual Range,Digital Clamp Meter,Manual Range Clamp Meter,Digital Clamp Meter Auto Range from Clamp Meters Supplier or Manufacturer-Guilin Huayi. To test one set of diodes, contact one ohmmeter probe to terminal bolt and contact each of 3 stator lead terminals with other probe. 1) do not use any bias voltage applied to the diode, but in photoconductive operation (Fig. Hope this helped a little. The alternator charges one designated starting battery and a bank of two designated house batteries. Etekcity Digital Multimeter, Amp Volt Ohm Voltage Tester Meter with Diode and Continuity Test, Dual Fused for Anti-Burn 4. Diode Measurements 1. Repair Manual - Troubleshooting Procedures How to Troubleshoot the 10Si and 15Si, Type 116 and 136 Alternators. Simple Unsolder, Press out & replace Regulator Blown - Buy replacement Stator Coils Corroded or Shorted/Open or bad solder joints. Modular design for easy servicing. Answer C is wrong. The assumptions I will make here is that the alternator is a 3 pole alternator that requires a diode lead attaching to the centre post and earthing. " However, an ohm-meter should initially show a low "resistance" (until the capacitor charges). If the battery and AC output are OK, replace the regulator/rectifier by process of elimination. Here's a simplified diagram. rectifier (diode), regulator/rectifier or stator. That's one thing I liked about the separate old school voltage regulator and alternator combo's. This can cause some of the more noticeable warning signs listed above, such as dim lights or failure of electric windows. Look for voltage between 13. Matco Tools Parasitic Drain Tester and Low-Current Probe helps diagnosis electrical problems with accurate information, keeping your Pontiac in running shape. (Sounds like 10. Start pulling fuses until the draw goes low. To order the Owon B35 click here These diagnostic steps are used to help locate electrical problems in a number of different sources. i did however check voltage the same way and got 10 or 11 volts does that mean i have a drain? thanks for. There are various methods used to test alternator diodes: ohmmeter, testy light, diode tester, and a scope test. Do you just need to remove connections? But ok to leave in place? 2. There was some oil around the plug on the back of the alternator so I unplugged it sprayed some electric plug cleaner but same thing keeps happening (testing for bad diode). But in this case, as well, you will have to set the dial to the point at ohms range values, where the diode is indicated and attach the two leads with the two points. The multimeter then displays the voltage drop when the test leads are connected across a diode when forward-biased. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0. The best way to identify alternator problems is by conducting a bench test. If it conducts in both directions, it is shorted. " However, an ohm-meter should initially show a low "resistance" (until the capacitor charges). The bridge is located in and fastened to the alternator case. Your alternator will charge the meter's input capacitance to peak voltage several times each revolution and that's what you meter will report. Before starting to troubleshoot an electrical problem, make sure you get yourself a good multimeter. Charging System Service Chapter 31 Objectives Measure and interpret voltage drops on the positive side of the charging circuit Measure and interpret voltage drops on the ground side of the charging circuit Test and repair an alternating current (AC) generator Diagnose voltage regulator problems Introduction This chapter discusses testing and repair of common charging system problems Principles. MEP-802a Low Alternator Voltage Output If this is your first visit, be sure to check out the FAQ by clicking the link above. Basic multimeters measures voltage, current and resistance, while more elaborate multimeters, such as the Fluke 78, or Fluke 88 have featues that can. Diodes used on modern alternators can usually handle the high voltage. Besides the possible damage to a good alternator, if the alternator is not producing full voltage, but just enough to keep the engine running, you'll never know it using this method. The Alternator should now produce a battery voltage between 14. 1) Remove sensing diode block from the alternator before making tests. terminal on the back of the alternator, (not at the battery). The bridge is located in and fastened to the alternator case. This rule is used to determine the direction of current in a generator’s windings. I have seen known bad batteries and alternators test good and vice versa. Using a multimeter on the diode setting, test for continuity on each side of each diode. Measuring low resistance is tricky with a digital multimeter. Attach the positive lead of the multimeter to the alternator's external housing. Regulated voltage on black scale. As pointed out by @tlhIngan, use a multimeter to test the alternator. Put the ohm meter on the old and new replacement diodes and got the same results when doing a continuity test; current. The other three diodes could be bad, but I can't see any way to test them without opening the alternator up. The meter should not read anything on any of these. A multimeter is an electronics testing device that, um, tests multiple things, including resistance, voltage, and current. Then check the voltage across the two small terminals at the alternator. ” Profiling alternators For Wendt, regulating the output of an alternator is as much art as science. This is done because if we join the diode in the opposite direction then it would short the circuit as the gate doesnot allow electricity to pass through it. It could still be bad. In the photos of this article we used a more expensive Fluke multimeter. New In-Depth Outdoors TV episodes return this Fall, Sundays at 8. Once connected to a terminal, an alternator should test between 12 and 13. Test the three diodes with the diode test. An alternator diode is being tested using a DMM (digital multimeter) set to the diode check position. diode take 2 to 3 weeks to drain a battery? Keep in mind I use the car apporx. These are very accurate and will measure the amp output within one tenth of one amp. The ohmmeter is the most common testing tool used when the alternator is disassembled. A car alternator recharges the battery and powers certain electrical systems. 6 (2oo1)alternator Charging at 14. RR Part Number 31600-MCW-D61 Here's the Readings. > great for testing alternator internals, the ohmeter was powered by nine > volts which was more than enough to bias the PN junction to test the > diodes. Alternator troubleshooting tips. If the AO (alternator output) is disconnected when charging, sometimes it fries diodes. As I mentioned in my second post, you can also use it to load test a battery. How to test an alternator part rectifier diode pack parasitic battery drain. Forward voltage will indicate 400 to 700mV. The diode rectifies its output (serving a function similar to what brushes would do in a DC generator). A quick way to check is by using a multimeter. New Voltage Sale. 99v minimum. He said if I removed the alternator they could run another test on it to make sure it was the diode. Page 11 Testing Procedures Plug the RED test lead into the "mA" or the "DC10A" jack of the multimeter, as applicable. Use a multimeter with a diode check function. A fresh diode pack (it's a Denso alternator) and the AC is down to 50-100mv by 4k. Use a multimeter  and set it to voltage. The AC ripple will cause havoc on the electronic brain. Get shopping advice from experts, friends and the community! No. Another problem the alternator can have is excessive AC voltage output. To use the diode test mode of the multi-meter, simply move the dial to "diode test" and make sure that no voltage exists at the diode (this may require discharging the capacitors to get rid of any voltage in the system). Set multimeter to diode check mode. To test a forward biased diode, place the positive probe onto the diode and the negative to ground. It is great for troubleshooting engine issues, such as dwell angle and dodgy alternator diodes, as well as for diagnosing mains electrical faults and basic electronic component failure. If your DMM has a "Didoe" setting, use that and compare readings - they should all be the same. 65 volts but then leveled out and did not come near 14 volts or above. The alternator should be replaced if AC voltage of more than 50mV is detected (in some cars as much as 100mV is acceptable). This is because a digital multimeter, unlike an analog multirneter, requires a power supply for the LCD meter and internal circuits. Use care when disconnecting the alternator output wire. Start the bike and measure the AC voltage across each of the 3 phases (wires 1-2, 2-3, 1-3). Test EB & CB junctions as you would test individual. A bench test will check the diodes and internal regulator and then tell you if the alternator is capable of producing its rated current and voltage. Bad diodes will cause a fluctuating voltage which the multimeter will pick up as AC voltage. 8 volts depending on the manufacture and the internal regulator fitted to the unit. The test equipment is expensive, however it is fast and easy to use and able to pinpoint the cause of the problem. To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. Set the multi-meter on 10 volts DC this time (remember the rectifier converts AC out of the alternator to DC going to the battery). I was hoping there was a way to test it in-situ. Bench testing an alternator on a test stand should verify whether or not its output is within specifications. AIRCRAFT ALTERNATOR MARINE 12 24 36 VOLT DIODE TESTER LYCOMING CONTINENTAL USA. Drawings and Notes on the Delco 10 SI Alternator from Al at AutoReWire. Boat Alternator Problems, Possibly Diodes I have an old sailboat with a Yanmar 3QM30H 3 cylinder diesel and a Yanmar (Hitachi LR135-31), internally regulated 35A alternator. Automotive alternators have diodes to rectify AC power to DC. DMM should read OL again. Then measure alternator output at several RPM's writing down RPM and volts. This is a test that you can do with the alternator still in the vehicle and in this article I'll show you just how to do it. Richpin demonstrates how to test an alternator with a standard multimeter. To test your alternator, follow these simple steps. It does NOT check the D+ diodes. Anybody know where I put my meter leads to test alternator charge and what 5 volts across the solenoid means?. I then calculated a possible internal current limiting resistance. Discard 392606 diode harness supplied with new engine. If that alternator is weak you'll notice a drop in fuel economy because the fuel system tends to go rich as a battery dies. Duplicates the circuitry found in an automobile. Peakmeter Pm2008a 2000 Counts Lcd Display Digital Clamp Multimeter Continuity Diode Testing With Auto / Manual Range , Find Complete Details about Peakmeter Pm2008a 2000 Counts Lcd Display Digital Clamp Multimeter Continuity Diode Testing With Auto / Manual Range,Digital Clamp Meter,Manual Range Clamp Meter,Digital Clamp Meter Auto Range from Clamp Meters Supplier or Manufacturer-Guilin Huayi. Basic multimeters measures voltage, current and resistance, while more elaborate multimeters, such as the Fluke 78, or Fluke 88 have featues that can. A new replacement Valeo alternator for the Porsche 356 Speedster pictured above comes in around $600 to $800 depending on the year. anything more than 1vAC is indicating a bad diode pact or rectifier pack on the alternator. Connect one lead to diode pigtail and other lead to base of diode. Test the three diodes with the diode test. A quicker way to test your stator is firstly to measure it's resistance, it should be about 0. Testing Electrical Systems with a Digital Multimeter Perhaps the most important tool you'll use in troubleshooting auto electrical systems is the multimeter. However for the meter this might have no notable effect except a little stress-free working due to the controlled voltage level. ALTERNATOR FAULT FINDING. However, you lost the reference voltage from the chassis battery. Use a multimeter  and set it to voltage. The alternator will still produce DC current, but when tested on an alternator test machine, it will fail the diode test. The voltage should, read between 13. DC ALTERNATOR DIODES AND CAPACITORS. I am a retired Chrysler engineer that designed and developed many electronic components for Chrysler and Dodge. Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. Rectifier testing and troubleshooting. But I am having the opposite problem. There are various ways of testing an alternator without the need for a multimeter. testing an alternator will conclusively confirm the presence of bad diodes or failed windings, the value of measuring or viewing ripple exists mainly as a quick test. With the motor running, turn on everything you possibly can in the truck. JBT and AST testing units have been designed to interface with modern “smart alternators” that communicate with the vehicle’s computer. Use the included test leads to perform other electrical tests. I used a diode rather than the indicator lamp. Does this apply to all Alternators. You can use any multimeter to test whether it is functional, but a digital multimeter with a diode check function will give best results. You can solve the problem at least temporarily by adding a small diode - see the shematic on my Web page. diode take 2 to 3 weeks to drain a battery? Keep in mind I use the car apporx. How to test your alternator. Test the rectifier diodes as shown here: Regulator theory:. A typical diode failure will show an asymmetric wave instead of a stable waveform. An alternator diode is being tested using a DMM (digital multimeter) set to the diode check position. 5 volts to 14. Reverse the meter leads and note the meter reading. As I mentioned in my second post, you can also use it to load test a battery. To test your alternator, follow these simple steps. Checking for a bad alternator diode is as simple as watching for flickering headlights, brighter than normal light bulbs, slower than normal engine cranking, and/or overnight draining of the battery In the blog, "How to Test an Alternator for Problems" by Dan Ferrell, he outlines a few simple procedures for quick-testing alternator diodes. 5 milliamps. Set the meter on “Diode Test” Mode by turning the rotary switch of multimeter. Start the bike again and you should be reading 7. The following test will be performed using Digital multimeter, Tool #19464. If you lose a single diode, the alternator would behave in just this manor. You can quickly determine if the alternator and battery are functioning properly by performing simple tests. Diode Test 1. There’s also another way to check the alternator manually. Here's a simplified diagram. In part, this is because the airborne alternator is tasked to conform to two very differ-ent profiles. 3 DC Megger Test-Use a hand-cranked or battery operated Megger to test the diode. Place one test probe on diode place and contact each of the three stator lead terminals with other probe. 551 ohms / OL An alternator could test as producing low-than-normal output, yet be okay, if the ____. Do the same with the black test lead but connect it to COM and run the meter. To find out if the isolator is sending charging current to your batteries, start your engine and check the voltage at the center post that comes from the alternator. Testing Alternator/Battery Voltage. Then check the voltage across the two small terminals at the alternator. The multimeter usually has a diode test function: When the test probes are connected as shown the meter gives you the diode voltage drop, it the probes are switched you'll get an open connection indication. Leaky diodes will generate AC ripples along your electrical system. FAULT FINDING MANUAL For Self Excited and Separately Excited Generators. Set the meter on diode test mode. To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. Users Manual, test leads, inductive pick-up and protective carrying case included. 3 volts (engine running, lights and accessories off). Feed the positive (about 18v) via the resistor to the zener on a heat sink and measure the voltage across the zener. When current dramatically increases, the voltage point on the diode forward V-I characteristic curve is called the A) Breakdown voltage B) Knee voltage C) Barrier voltage D) Both B) and C) are true. Retrieve Doc. Test a rectifier bridge or a diode trio with an ohmmeter. Dunno about the meter. Here's what to do. Need Advice on Amp Meter w/Alternator reading do my testing with a voltmeter hooked to the battery. There are various methods used to test alternator diodes: ohmmeter, testy light, diode tester, and a scope test. You're measuring the collective voltage drop across ALL diodes in the alternator. Just test it with a multimeter. Once connected to a terminal, an alternator should test between 12 and 13. The DC Charging current is 0, charging light 9. 4L equipped car, pick up or SUV, is a simple test that can be done with just a multimeter. With the engine at idle, multimeter monitoring the battery voltage, wiggle the engine harness starting from the battery area all the way to the ECU and see if you could duplicate the concern. Test the alternator with a voltmeter Alternator test with a voltmeter If it's in the range, it's good. Alternator Circuit Test Procedure Sample Printout EXP-1000HD Features From battery, starter, and alternator diagnostics to circuit integrity testing, the EXP-1000HD is the most versatile and reliable electrical diagnostic tool on the market today. 481, and with the meter negative on the center terminal, the reverse bias was infinity, so the isolator checks good with this test. Any suggestions on how to test to determine whether it is fixable and if so where to get basic parts like brushes? Last time I took a MM alternator to an auto electrician they just started swearing about landrovers, so not keen to repeat that. This is called a 'soft start'. A reading of 13. Test A) Try a decent service station, they may be able to test the alternator, the simple battery test is a large industrial volt meter and amps guage, this will give the battery static voltage , they can then flick a switch that will simulate a load eg 20 amps and the voltmeter will dip in its reading, the more it dips the more unstable the. Dying alternator? -- Fails load test. 6) Now, Maintain the 1500 RPM and Turn off the Headlights. First make sure that the vehicle's battery is fully charged. When using an ohmmeter or a test light, the diodes must be unsoldered and isolated from each other. The good news is that replacing a factory alternator with a high output alternator, in and of itself, isn’t going to damage the rest of the electronics in your car, even if the new alternator is much, much bigger than the old one. Check the integrity of the regulator diodes on a Bosch alternator by using a multimeter to measure the voltage readings at the D+ terminal and B+ terminal. 2 Fluke Corporation Smart troubleshooting pinpoints rectifier failures Gengler cites the three possi-ble states of a diode and how to identify them. I tried testing it and alternator was charging a little, but not where it was supposed to be One question does the car still run if the car is on and you remove the battery? I was going to test it that way, however I know there are warning messages when trying to jump a car and such, so I didnt know if the car will yell at me. 4 out of 5 stars 2,172 # 1 Best. Simple Unsolder, Press out & replace Regulator Blown - Buy replacement Stator Coils Corroded or Shorted/Open or bad solder joints. Kit Autotronic 2011 An alternator is basically a generator but instead of running on fuel an alternator in a car converts Set the meter on ‘Diode Test. Test the three diodes with the diode test. and the Black lead of the meter on the body of Alternator as indicated by E. Connect wires one at a time to see what lead is drawing current. If it’s in the range, it’s good. Do not unplug from alternator to run test. Switch your multimeter to the lowest AC setting and reattach the test leads to the battery. To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. 8 when tested against itself From the cannon plug to: Alternator-4. If the wir - ing is OK, have the engine’s charging circuit serviced by a professional. Diodes Blown - (Multimeter Test on Diode Function for shorts / open. Just FYI, automotive alternators have a diode pack also, and when one of those 3 fail, the vehicle's battery will discharge through the alternator. The reading is near the maximum amperes you made a note of earlier. OK, the test is divided into three parts: PART 1- Testing the alternator voltage output with the multimeter in VOLTS DC mode. Perform an alternator stress test by turning the car’s headlights, radio, and air conditioning unit on. Use care when disconnecting the alternator output wire; make sure the battery is disconnected first. The test will require you to disconnect main fuse B. Test the Alternator Diode; To check for a bad alternator diode, you may want to reset your voltmeter to the lowest possible AC voltage scale setting. Set meter on ohm scale. Testing can become a little confusing to explain so I’ll break it down into numbered steps. Note the bulb or reading. I think I need to then make my system neg to ground/frame. Let's throw that illusion out, start with a clean slate and learn your motorcycle's charging system in the most simple and basic way possible. your coments please. If the alternator is working at all the voltage should be above the 10. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0. Has to be your meter. Further testing will be necessary. Topic Progress: ← Back to Lesson Description: Bench Testing Alternator Components Video Clip from Bergwall On Demand’s A6 Electrical / Electronic Systems ASE Test Prep Video Course. Repeat this same procedure between the the AC inputs and the "negative" output. HOW TO TEST MY ALTERNATOR? Connect the meter leads to the battery terminals and look for 13. Reverse the test leads) and note the measurement. to you by the instructor test the alternator using the ARBST tester. Test the three diodes with the diode test. Therefore 2 diodes could be connected from an alternator output terminal, one to each of 2 battery banks. Alternating Current (AC) Ripple Test #1 If the engine electronics seem to be performing erratically, it is possible that you might have one or more marginal diodes in the alternator that are leaking. The Diode Test procedure is conducted as follows: Make certain a) all power to the circuit is OFF and b) no voltage exists at the diode. Diode Test: Remove the brown wire and diode from the field terminal of the alternator and set the multi-meter to the Ohms setting. However, you lost the reference voltage from the chassis battery. You need to trace the short before you can perform the following tests. Measure battery voltage with the engine off using a multimeter set to dc volts range. Forward voltage will indicate 400 to 700mV. Place one test probe on diode place and contact each of the three stator lead terminals with other probe. This type of test equipment is a good investment for a repair shop, however an alternator can be checked with the use of a reasonably priced volt-ohm (VOM) meter. International elec-trical symbols used on the meter are shown in Table 1. The photographs below indicates that this diode tested good. The usual culprit is the two wire plug on the alternator, but a failure of the isolator diode or a broken wire will give the same result. When the aircraft. There could still be a problem with your alternator, but get the diode installed correctly first. Close adherence to the following repair manual in the order presented will lead to the location and correction of charging system defects in the shortest possible time. It is great for troubleshooting engine issues, such as dwell angle and dodgy alternator diodes, as well as for diagnosing mains electrical faults and basic electronic component failure. The meter then needs to be chnaged to diode test mode to test the rectifier positive diodes. This type of test equipment is a good investment for a repair shop, however an alternator can be checked with the use of a reasonably priced volt-ohm (VOM) meter. Alternator output on green scale. 3 wires connected to the Bat terminal on switch. In this post, I am going to teach you how to test a relay with a multimeter. If you hear the buzzer while using this multimeter, it means that the resistance is less than 40 ohms. terminal on the back of the alternator, (not at the battery). Bad diodes will cause a fluctuating voltage which the multimeter will pick up as AC voltage. To test one set of diodes, contact one ohmmeter probe to terminal bolt and contact each of 3 stator lead terminals with other probe. Remove the plug from the back of the alternator using your Multimeter, set on DC volts, connect the black probe to a good earth and test each terminal in the plug in turn with your test probe. The diode rectifies its output (serving a function similar to what brushes would do in a DC generator). AC, high beams, radio, emergency flashers, all of it. 05Megohm, diode test mode OPEN Alternator is working now. The OEM rectifier is pretty easy to spot, even if they respray it. connect an amp meter between the cable and terminal. The bad diode can cause the circuit to charge even when the engine is shut off, and you end up in the morning with a car that won't start. Testing Procedures Place the RED test lead onto one side of the diode being tested and the BLACK test lead onto the other side. It has inductive spark plug hook-up and test leads. A fresh battery and a malfunctioning alternator, however, will quickly leave you stranded again. It should be somewhere from 13. Testing can become a little confusing to explain so I’ll break it down into numbered steps. The diodes are easy to test with a multimeter. Do I have to have power running through the board to test it or does the meter supply?. Also, as far as I know, the car has its original alternator so its old. with AC volts the measurement should be 0. Free run starter draw on red scale. Alternator AC Ripple/Diode Test using a tester with a scope. In this post, I am going to teach you how to test a relay with a multimeter. If the alternator had a worn brush it would have low or no output. Any simple diode will exhibit a 'front-to-back' ratio since they are designed to allow current to flow in only one direction. You can quickly determine if the alternator and battery are functioning properly by performing simple tests. replacing a 20dn, 30dn, 41 dn, and d. Do not unplug from alternator to run test. Your alternator can also have a bad diode, which causes the circuit to charge even if your engine isn't on. Otherwise the safety features provided by the meter might be impaired. A good diode will read _____ if the leads are connected one way across the diode and _____ if the leads are reversed. The multimeter should read a resistance of infinity meaning it blocks all current flow. Different variations of Alternator and Battery are used on different models. Just test it with a multimeter. With the multimeter set to measure resistance, it should measure more than 550 ohms if the alternator diode is any good. unbalanced by multimeter, at no load voltages indicate loose neutral connection / stator winding problem 4 check no load excitation voltage ( dc any problem in alternator will increase the voltage output of avr) excitation voltage, avr sensing input & diodes at rra to be checked.