Alternator over charging battery 65 396(NOM)

[Nick F.]

After doing a series of tests to the alt/reg/battery circuit and after replacing a spent alt, bad regulator and a cooked battery, I'm still no further ahead!
I installed a new Die Hard Gold battery today with 12.96 VDC. Hooked up my voltmeters to the alt wiring and one to the battery terminals to watch voltage. I started the car and the charging began at 13.2 but the higher the RPM, the higher the voltage, all the way to 19+. I shut the engine down and started running all the tests all over again. I ran continuity on all wires to and from the alt back to regulator. The "F" terminal (dark blue wire) was good, the "R" terminal (black/white wire) good, red terminal was good also. I found that my #4 wire in the voltage reg plug (black/pink wire) has continuity with any ground I touch. I disconnected the firewall connector and had continuity from regulator to firewall connector pin. However, no ground condition in the engine compartment. Does anyone know where the BLACK/PINK wire goes once it crosses under the dash? Apparently, something inside the car is causing a ground condition which somehow keeps my alt in the high charge mode.

[Bob H.]

Re: Alternator over charging battery 65 396(NOM)

Hi Nick:

I believe that wire goes to the system wide harness ground and the ground you are reading is correct.

Are you sure the regulator hasn't croaked again? I don't know what you are using but I would test with a cheap $12 electronic one from a parts house.

It sounds like you changed everything but the regulator would still be what I focused on.

We need some more information. First, was this system working ok and then something failed or did you buy it in this condition? That would give us a base to work from. What alternator are you using? Hopefully, someone did not give you one that is internally regulated, etc.

We will probably need to get voltage readings. I assume you have your battery voltage appearing on the bat of the alternator and the red lead on the reg. Also, that you do read ground on the alternator black lead and base of the reg.

[Nick F.]

Re: Alternator over charging battery 65 396(NOM)

Hi Nick:

I believe that wire goes to the system wide harness ground and the ground you are reading is correct.

Are you sure the regulator hasn't croaked again? I don't know what you are using but I would test with a cheap $12 electronic one from a parts house.

It sounds like you changed everything but the regulator would still be what I focused on.

We need some more information. First, was this system working ok and then something failed or did you buy it in this condition? That would give us a base to work from. What alternator are you using? Hopefully, someone did not give you one that is internally regulated, etc.

We will probably need to get voltage readings. I assume you have your battery voltage appearing on the bat of the alternator and the red lead on the reg. Also, that you do read ground on the alternator black lead and base of the reg.

Hi Bob,
I had the trans out for repair, got it back together after 3 weeks and that's when my 65 BB started having charging issues. It started with hesitation that day and it supposedly ran fine up to that point, started ok, ran fine everyday. I had never touched the electrical system for the 4 months I've owned the car. I noticed driving home that the car was missing terribly. I parked it in the garage and the next morning, battery was dead. I jump started with my pickup truck, checked battery voltage before (was 9.99), then jumped started it after 25 minutes of charging checked voltage while running, only 10.6v. I put a trickle charger on it all day. I figured alt was bad but remembered these old cars had a regulator too. I began running alt/regulator tests as posted by one of the other members on the Corvette forum. I have 12.26vdc at the batt stud on the alt and that compared to the voltage at the battery of 12.26. After disconnecting the alt wires & reg wires, I checked continuity of all the wires from the alt back to the regulator, including the ground from alt to reg case, all was fine. First, I've replaced the alt twice (ext regulated) and then went to a SS reg from Autozone. When I start the car, the voltmeter just stays at battery voltage even when turning lights on.
What I did notice is that the battery was completely dry, it got cooked probably big time along the way. (I should have checked this first, somehow overlooked the electrolyte level, duh...). I saw sparks coming from the plastic plug on the alt only to see that the "F" prong was grounding on the case (hence the 2nd alt replaced). I also found that the "F" (blue wire) and "R" terminals on the plastic plug were reversed (bubba did this before me). When I change them back to what they should be (blue to "F" & "R" to terminal 2 on reg), the alt started charging as indicated by the voltmeter across the "batt" terminal & ground on the alt and a voltmeter at the battery terminals. However, as I accelerated the engine, the volt reading kept going higher and higher with rpm gain, got to 19+v and I shut her down. I'm assuming that the shorted "F" terminal at the alt short out the SS regulator. Surprisingly, my battery didn't explode or the car caught major fire!!

[Jack H.]

Re: Alternator over charging battery 65 396(NOM)

This hasn't been mentioned as far as I can tell, but flip your copy of the AIM to UPC 12, Sheet A8, and look at View A. You'll see there are TWO ground wires that attach to the horn relay.

One (upper) runs to the engine wiring harness while the other (lower) runs to the outside case of the V-Reg. You'll also see a note referencing UPC 6 associated with this second ground wire.

If you flip to UPC 6, Sheet B4, you'll see ONLY the V-Reg to Horn Relay ground wire (Item 5). It's a SHORT guy.

If you've built the car without doing it per the AIM, your V-Reg could have a faulty ground reference with the charging system acting like Dr.Jeckyl and Mr. Hyde as a result...

[Wayne M.]

Re: Alternator over charging battery 65 396(NOM)

...... I ran continuity on all wires to and from the alt back to regulator. The "F" terminal (dark blue wire) was good, the "R" terminal (black/white wire) good, red terminal was good also. I found that my #4 wire in the voltage reg plug (black/pink wire) has continuity with any ground I touch. I disconnected the firewall connector and had continuity from regulator to firewall connector pin. However, no ground condition in the engine compartment. Does anyone know where the BLACK/PINK wire goes once it crosses under the dash? .....

Nick -- providing you've followed Jack H.'s volt reg base grounding info, that 24 gauge black/pink stripe wire (24B/P on wiring diagrams, and #4 on the volt reg plug) goes to the firewall connector (inboard plug, top ouboard pin). On the other side of the firewall, it becomes 20BRN (20 gauge brown) which goes to a junction of 4 other brown wires, all fed from a 14BRN wire coming from the ignition switch accessory terminal, which is live when key turned to ACC or when in run/ignition position. IMO, should NOT be showing voltage or ground when key in OFF position, and has certainly nothing to do with voltage regulation function within the VR, as it controls an on/off field relay solenoid (not the voltage regulating double contact solenoid).

[Nick F.]

Re: Alternator over charging battery 65 396(NOM)

This hasn't been mentioned as far as I can tell, but flip your copy of the AIM to UPC 12, Sheet A8, and look at View A. You'll see there are TWO ground wires that attach to the horn relay.

One (upper) runs to the engine wiring harness while the other (lower) runs to the outside case of the V-Reg. You'll also see a note referencing UPC 6 associated with this second ground wire.

If you flip to UPC 6, Sheet B4, you'll see ONLY the V-Reg to Horn Relay ground wire (Item 5). It's a SHORT guy.

If you've built the car without doing it per the AIM, your V-Reg could have a faulty ground reference with the charging system acting like Dr.Jeckyl and Mr. Hyde as a result...

Jack, thanks for the info. I did check the grounds, both of them and they were both fine.

[Nick F.]

Re: Alternator over charging battery 65 396(NOM)

Guys, SUCCESS finally! After going thru the alt/regulator/battery tests 3 more times, I was convinced that the regulator, even though I replaced, must have shorted out when the first alt begin sparking at the "F" terminal. I replaced the regulator and walla, the alt starting putting out 14.56 vds and didn't exceed 16v even at high revs, lights on heater on, stayed at 14.75 throughout.
THANK YOU ALL who responded and gave me some insight into a 45 year old car. All in working order, at least for today....tomorrow's another day!

[William C.]

Re: Alternator over charging battery 65 396(NOM)

Assuming you are replacing the regulator again (or have already) if trans work was done, did the starter get pulled? The charging system uses as a reference point a connection via a large ring terminal on a black wire under one of the starter to block attachment bolts. If that is attached to the incorrect location, or not attached, it will cause the regulator to drive the alternator very hard. Lots of invo on this in the archives, but that is where I'd start looking for my "lost" ground.

[Bob H.]

Re: Alternator over charging battery 65 396(NOM)

Glad to hear it!!. At least the new ones are cheap.

I just found a correct late 66 one on Ebay for my car. Very hard to find and this one was ugly as sin and no one bid on it!! When I got it, it works perfectly. After detailing it, I'm set. (think I'll carry a spare just in case)