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WesTXmc 11-27-2011 09:14 PM

Strange GM Regulator/Alternator Problem
Evening fellow Hot Rodders. I'm working on a 1970 Monte Carlo. Here's the problem:

Key on - no "Gen" light.

I have 12+ volts on 3 of the 4 wires at the regulator plug with it plugged into the regulator - I also have 12+ volts on the regulator case (regulator case not grounded to the chassis)? I found this when I was hooking up the battery - I had my test light hooked to the battery ground and the tip was sticking in a bolt hole on the rad support. As soon as I hooked up the positive battery cable and turned the key to "on", the test light lit up. I tracked it down to the regulator case - bolted to the rad support - and when I removed the regulator from the rad support, the test light went out. It will do this weather I have the 2 wire plug at the alternator connected or not to the alternator.

Car starts and runs fine but I have 16+ volts on the gauge and a meter?

Changed the regulator - same problem. Do I have a problem in the alternator? Why isn't the "Gen" light on with key "On"?

Any ideas, comments, questions, etc is greatly appreciated. Thanks in advance.


66GMC 11-27-2011 11:08 PM

Terminal Identification:
F= Field (F terminal on alternator)
2=Stator (R terminal on alternator)
3= B+
4= Light

The regulator is grounded to the rad support. I suggest that you check the ground connections from the regulator to the rad support, rad support to frame, and frame to engine.

Use of those uninsulated braided straps is a good idea at any point that has a moveable joint (like a hood or trunk lid) ... or any part that may be rubber mounted (i.e. rad support, truck pickup box).

NAPA (Echlin) Part Numbers if you happen to need them:
VR142 Voltage Regulator
VRC142 Voltage Regulator Connector
VRA142 Alternator Connector

EOD Guy 11-28-2011 03:46 AM

1 Attachment(s)
Is your bulb burned out? IF your getting 16+ volts with a new reg..... might be your alt. Get it ck'd at the parts in a box store. If it is and you're gonna get a new one....might think about converting over to an internal regulated alt..... super easy to do and possibly the best thing I've done for my old girl. Basicly putting in two jumpers, a new pig tail and throwing the old reg away.

Remove the wires from the regulator plug, Splice the Blue wire to the brown wire. Splice the white wire to the red wire. Change out the Alt pigtail. Run a new 10 (8 peferably) gauge wire from the Rad support junction splice over to the horn relay. I was amazed at how bad the orig wire on mine was melted/deformed, I replaced it with 2ea 10 gauge wires from the junction to the horn relay.......good to go.

WesTXmc 11-28-2011 07:09 PM

66GMC - It was a ground issue. I installed new rubber bushings under the rad support - no ground to the support with the rest of the front clip off. I ran a ground strap from the battery to the rad support - problem fixed. I have 13.98 volts at an idle. Still no "Gen" light. I checked the bulb and it does work. The printed circuit on the back of the instrument cluster looks a little frazzled? I removed the dash pad to access the bulb and have limited access - I'll have to pull the instrument cluster and see if there is a bad spot in the circuit.

EOD Guy - I was thinking the same thing - read a bunch of threads about the swap ast night and was planning to do just that if I could not solve the problem. It's definitely going to happen the next time the alternator/regulator gives me any trouble.

Thanks guys for the replies - very much appreciated! :thumbup:


EOD Guy 11-28-2011 07:14 PM

Good to see you got it figured out!

66GMC 11-28-2011 07:21 PM


Originally Posted by EOD Guy
Good to see you got it figured out!

X 2 :thumbup:

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