I had to pull the engine to replace the rear seal and fly wheel. Put everything back in, started the car. Everything is fine except the volt meter is showing -10 volts and the red light is on. Checked the ground strap and the alternator harness plug and it seems ok. The alternator was new when I rebuilt the motor and worked fine when I pulled the engine.

Can you run a wire from the battery to the volt meter? Or put a multimeter on the battery?

I would also mention how cheap an upgrade to a solidstate voltage regulator is...

I have a multi meter, what am I looking for?

Voltage at the battery terminals with the car running.

Should be ~13.5 ish. Anything over 12.8-ish means the alternator and voltage regulator are working (though 13.5-ish is much better).

Is the alternator plugged in at the relay board? Or did you knock the voltage regulator off it’s plug?

Yeah, start with voltage at the battery then check those connections van b mentioned. You have to make certain it's not grounding issues up front. Although the g light makes that less likely.

If you are low at the battery I am sure it is what van b said or poor grounding of the fan shroud/alt connections.

The G light will come on anytime voltage is sensed to be less than specified. I think it’s 14v but I’d have be check for sure.

I learned this because when I did a 30f cold start last month, my light was on when the idle was super low. As soon as I blipped the throttle, the light went off. So I figured the cold engine and low idle on that initial start meant the alternator wasn’t able to make enough voltage.

Could the battery have taken a dump?

Could the battery have taken a dump?

same problems

With mine I had the usual low voltage on the meter and it did a really good job of showing me if my brake lights or turn signals were on. I now have it running straight to battery (with a fuse and a relay, the relay being activated by the old voltage hook ups, so no cutting original wiring etc). After that the voltage showed exactly what was going on at the battery. I was still a little low 12.3-12.8ish so I replaced the regulator with a NOS unit. Still a little low 12.6-12.8ish occasionally up to 13. I replaced that with a solid state regulator and now it sits in the mid to high 13s all the time.

Check your grounds. Battery strap, braid from trans to under the trunk, and the stud from under the relay board.

Zach

@buddyv Robert just went through this very thing. In his case, a new voltage regulator solved it, I believe. Robert, can you recap your experience?

for me when this happened it was a grounding issue, recheck you harness ground on body under the relay board and your transmission ground strap. i didnt tighten that down all the way and that was the issue on that occasion. it seems unlikely your voltage regulator just failed on you suddenly but maybe its not in tight either.


Phil

I'm looking at a Sierra Madre Voltage Regulator Hella PN 901.603.206.02-HEL - How do I know if it is a Solid State Regulator? and where can I find one?
Thanks

Check the voltages at the alternator. There's 3 wires accessible at the connector from the alternator to the relay board at the relay board. Measure each wire to chassis ground; not the engine case. See the diagram for the circled signals.

D+ to Chassis: Should be 14V, may not be much if the alternator is not active.
DF to Chassis: Should be 5-8V, may be zero.
D- to Chassis: This must be zero or close to it.

Did the red wire to the starter get put back on?

I think I found the problem. Just for the hell of it, I decided to check the plug connection on the voltage regulator. When I turned the key to the on position the volt meter would only go up to 10 volts. This is what I found. Ordered a new regulator and I have a spare relay board that I restored.Click to view attachment

The hella unit is the solid state version.

Be careful with the "new" voltage regulator. A bad one can cook your battery.

Describe what to replace under these conditions?

Battery voltage: less than 12.8V, replace battery?

Red wire: <14V, replace Vregulator? if >14V, replace Vregulator?

Green wire: if =<5-8 volts does this mean alternator not working at idle or what? if >5-8 volts, the replace alternator or what?

Brown wire: if >0 volts then dirty ground?

What are the symptoms if the alternator diodes are bad?

Bumpity.

Ordered 2 voltage regulators that were the newer black box design without the pigtail plug. One had a bent plug and the other would only go on half way as the mounting tab would not clear the side of the relay board. Contacted SMP and they apologized and recommended finding a NOS model. That should be coming, Thursday. In the mean time I am thinking everything worked before I dropped the engine, so why doesn't it work now? Went through all the connections and found the large red wire in the alternator harness was not connected to the starter. Hooked up the wire and now have 14 volts at the volt meter!!!

Oh man. That's rough.