66 overcharging alternator

[P.J. McGrath]

Hello All -
Suddenly last week the high beam indicator lamp and both turn signal lamps on my '66 all lit up at the same time (dimly). The ammeter guage also began fluctuating between + and -. While troubleshooting the problem I found that I am getting 17vdc at the battery and the fuse box while the car is running. I replaced the voltage regulator but this did not correct the problem. Is the high voltage causing the lights to illuminate or is some kind of short causing excessive draw from the alternator? Could the alternator be the problem? It is a rebuilt unit and has been on the car for about a month. It was putting out about 14 vdc when I installed it. I'll be tearing into it this weekend and hope someone may be able to point me in the right direction. Thanks - P.J.

[Jack H.]

Re: 66 overcharging alternator

For you to see 17 VDC across your battery, something is 'rotten in Denmark'... The charging system 'thinks' the battery is in a world of hurt and is working overtime to 'fix' the problem. This can happen for a number of reasons:

(1) The v-reg has gone bezerk and it's telling the alternator to over charge without seeing relief.

(2) The alternator has gone nuts and it's generating non-stop, FULL output.

(3) The battery has failed (one or more cells shorted internally), so regardless of charge delivered it won't pump back up to 'normal'.

(4) The interconnecting wiring is faulty and the key charging components aren't 'talking' to each other clearly and/or seeing things that aren't real.

To solve the problem yourself, you'll have to go one component at a time until you find the 'bad guy'. BUT, if you had the car at a local auto electric shop, they'd roll out their diagnostic cart, connect it to your car and fault isolate the problem in something like 10-minutes flat...

[P.J. McGrath]

Re: 66 overcharging alternator

Do you think the overcharging is contributing to the dash indicator lamps illuminating when they shouldn't be?

[Joe R.]

Re: 66 overcharging alternator

I agree with Jack that 17 volts at the battery is very unusual. Are you sure that this measurement is accurate?

I have not studied the wiring diagram, but it seems *highly* unusual for the indicator lamps to glow just because you have excess voltage. Something is very fishy. In order to light a lamp, current has to flow. A study of the wiring diagram might yield some theories as to how that could occur.

One thing I would suggest is that you make sure that your dash ground, alternator ground, voltage regulator ground, and battery ground are all reliably tied together. When these systems lose their common reference, strange things can happen. In a Corvette, all these grounds must be tied together with dedicated wires, since the body is fiberglass.

I recall reading a recent article (possibly by John Hinckley in Corvette Enthusiast, but I can't recall for sure) where the author described some common Corvette electrical problems. One such problem was the dash cluster "going crazy." As I recall, the typical cause had something to do with deterioration of the contacts in the harness connector at the firewall. I can look around for the article if you like.

[P.J. McGrath]

Re: 66 overcharging alternator

That voltage reading is on the money. I had been driving around during the light bulb episode and when I got home did some checking. The battery seemed unusually warm so I checked across the terminals and was getting around 17 volts. I was doing some troubleshooting earlier today and checked at the fuse panel. 17 volts there as well. I'm reading 13.5 with the car not running. It does seem strange that all three bulbs would illuminate. Each has it's own wire feeding the bulb and how likely is it that all three wires could get shorted at the same time. I've done some visual checks and don't see anything obvious. I've moved the harness as much as I could thinking it may be getting chafed somewhere. I tried removing all the fuses to see if I could isolate a particular circuit but the bulb/overvoltage issue continues. There has to be a short somewhere. The bulbs stay grounded and for them to illuminate they must be getting voltage from somewhere. I'll check for bad grounds though, I've seen that cause some unusual operation as well. I was hoping to avoid removing the dash panel. The two problems must be related somehow....P.J.

[Joe R.]

Re: 66 overcharging alternator

Don't pull the dash panel just yet. Other things are higher on the suspect list. There are other people on this Board more experienced than I am, so hopefully they will offer some insight.

I'd say that if there really is 17V across the terminals of your battery, you should focus on why that is happening. Fix that first and see if the wierd bulb problem goes away.

I presume that with the engine off and 13.5 volts at the battery, the bulbs do not illuminate. If they still illuminate, then you may have two problems to solve.

For the 17 volt problem, you have either a bad component or bad wiring in the system comprising the battery, voltage regulator, and alternator. The 1963 Shop Manual describes a series of diagnostic tests that you could try.

[Kevin M.]

Re: 66 overcharging alternator

Could it be the headlight light switch?

Kevin

[Gerard F.]

Check the battery first

You have probably already cooked it. At least before you pull the dash. If you are still getting 17 volts with a new or good battery, then check the voltage regulator and adjust it per your chassis service manual. There is also a resistance check on the alternator in the service manual, at least in the 67 manual. If all else fails take it to a shop as Jack suggests.

Jerry Fuccillo
#42179

[William C.]

Re: Check the battery first

I Can't agree more, that pulling the dash is the last step I would contemplate, and then only after I had double-checked everything in the Engine compartment twice! Battery, Voltage regulator, and alternator all need to be VERIFIED independently, as well as the wiring double-checked before tearing into a dash that worked properly before this problem arose. I believe NAPA and some other parts houses can check the individual electrical parts at their stores.

[Chuck R.]

Re: 66 overcharging alternator

I have experienced over the years many instances where electrical systems will lose the common ground and indicator lights and other ancillary lights will dimly glow as they were being back fed.

If this problem as suddenly appeard, I would start investigating the grounding aspects of the chassis before I started pulling components off the car just yet.

The wiring diagrams are pretty specific on just where the key ground components are located.

Just my two very corroded penneys worth P.J.

I hope it's a straight forward fix for you.

Chuck

[Gerard F.]

And the battery cables *NM*

[Joe C.]

Re: 66 overcharging alternator

My concern is WHY all the lamps lit up dimly. That may have been caused by a short in your turn signal harness, which may have been bad enough to fry your regulator. This will very possibly send full voltage to your alternator's "field" windings, resulting in excess output.
As mentioned above, bring it to a REPUTABLE repair shop for diagnosis. But remember, you've got to isolate the short first.

Joe

[Michael H.]

Re: 66 overcharging alternator

Chuck,

I think you're on to something here. The first thing I thought about was a bad or non grounded voltage regulator. If I remember correctly, this would cause either full on charge or no charge at all.

I would run a temporary ground wire from the engine to the 12ga black ground wire that's attached to the side of the voltage regulator. If this cures the charging problem, it's likely the ground wire in the harness is broken or not properly attached at it's other end. (starter) The regulator has to be grounded to work properly.

Alternators will charge as much as the regulator allows them to charge so I don't see any way the alternator could be the cause of the problem.

It's common to see a broken black 12ga wire at the starter. If all of the problems that you describe happened at the same time, it's very likely that one failure caused all. Remotely grounding the black wire at the voltage regulator should temporarily cure all if this is ideed the cause. Hope this helps.

Michael

[John H.]

Re: 66 overcharging alternator

I'd take a good look at the bulkhead connectors on the engine side of the fuse block, too; the high beam warning lamp and the turn signals get power from independent sources, and the only place those two circuits are adjacent (other than inside the wrap of the instrument panel harness) is in the outboard bulkhead connector.

[William C.]

Nice Clean Connections John!!! *NM*