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Posted by: arsprod May 1 2021, 02:07 PM

Charging light came on recently and I knew the car still had the original alternator. So instead of testing (assume) I just installed a new (rebuilt) alternator. Same problem - light's still on. Also replaced voltage regulator with solid state unit - didn't fix.

With the alternator disconnected from the relay plate the light goes off. I have 12v at each of the 3 pins for the alternator connector at relay plate but nothing from the (new) cable from the alternator. Please don't tell me I have another bad alternator... but do I have a bad alternator? I'm stumped. Ground straps all look find. Thanks!

Posted by: Spoke May 2 2021, 12:47 AM

With everything connected as it should be, with engine running, measure the voltage on each conductor on the alternator connector on the relay board. Connect the negative probe on the voltmeter to chassis ground, not the engine case. What voltages do you see?

Posted by: arsprod May 2 2021, 06:38 AM

12V at each on the relay board

Posted by: Spoke May 2 2021, 07:13 AM

Something is not right with your measurements. The 3 signals are DF, D+, and D-. Look at the diagram and notice that D- goes to the alternator and to engine case. The engine case should be a zero volts WRT the chassis and D- should be zero volts WRT the chassis as well.

Please provide some detail on how you are measuring 12V at each of these signals. Where is the negative probe of your voltmeter?


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Posted by: arsprod May 2 2021, 07:18 AM

Yeah, I've stared at this for awhile now. I keep coming back to bad or missing alternator ground. I know it's case grounded at the mounting bracket. I think I'll try running a ground wire from the pivot bolt to the transmission ground strap.

Posted by: ClayPerrine May 2 2021, 12:47 PM

If the alternator is bolted onto the motor, then it is grounded. If you want to verify it, using the ohm meter function, touch one end to the alternator case and one end to the engine case. You should get 0 ohms. Then repeat the process between the engine case and the negative battery terminal. You should again get 0 ohms.

Clay

Posted by: arsprod May 2 2021, 01:06 PM

Thanks. I check voltage on either side of the charging light and the blue wire side had like 1v. Pretty sure this alyernator's not doing anything. Pulled it off and taking to rebuilder to bench test. Fun!

Posted by: arsprod May 3 2021, 10:34 AM

Follow up, just returned from rebuilder. "Oh we're sorry, there was a broken wire." ARGGGHHH!