ALT and OIL light after key removed

[patrickdotryan]

Hi guys.

So. I did a full motor and engine bay rebuild. All wires are original and look very good. I installed a new voltage regulator and starter solenoid. The battery is new too.

If I start the motor, when I turn the truck off and take out the key, the ALT and OIL lights glow. Even with the key out. if I disconnect the battery and reconnect, the behavior stops. I can turn the key to ON and back off and it doesn't occur. But if I start the truck again then turn it off, it occurs again, I can pull the key out and the lights are on.

Any suggestions?

Thanks
Patrick

[Busboy]

My guess is that the alternator has a diode leaking back through the system. Try another alternator or disassemble the alt. and check the diodes with an ohmmeter.

[patrickdotryan]

Thanks busboy. Any clue if there's a way to check wiTh a meter at some point along the way before pulling out the alternator? Also, because I painted, is it possible that a bad ground might cause the same symptom? Patrick

[patrickdotryan]

Thanks busboy. Any clue if there's a way to check wiTh a meter at some point along the way before pulling out the alternator? Also, because I painted, is it possible that a bad ground might cause the same symptom? Patrick

[Busboy]

I'd definitely try just attaching by hand a jumper ground wire from the alt case to the block or battery negative terminal while the problem is occurring. although I find it hard to believe that the alternator wouldn't ground through one of it's mounting bolts.

[patrickdotryan]

Here's an update. I had bought a new repro voltage regulator from Macs auto parts. The kind that's USA made and looks period correct because my engine bay looks all nice. But just in case, I kept my old rusty one. Today I swapped the old one back in and lo and behold, ALT and OIL lights go out once the key is switched off.

Then because I'm thorough, I switched the new one back in. Problem occurs again. I have no idea how the voltage regulator works but it seems that this new regulator is causing the dash lights to stay on. The part number is identical to the old one but the old one works fine and he new one doesn't.

I'm hoping this is just s faulty one because I really don't want to keep my rusty old one.

Anyone shed any light on the issue?

Thanks
Patrick

[carnuck]

The regulator is the wrong one or mis-wired inside. Does your old one still function correctly?

[patrickdotryan]

Yes. My old rusty one works fine. I just bought the repro new one for cosmetic reasons when I re-did my engine bay. The new repro has the identical part number on it as the old rusty one. They appear identical. Apart from the fact that the old one works and the new one doesn't!

[bluef250]

New electric parts are commonly defective!

I'd clean up the old one, reinstall, and be done with it.

If Mac's were decent they would take the new one back. Good luck with that.