One Owner

I have read numerous old strings but cannot find the same issue; here it is.

Recently finished complete 69 vert restoration. Ammeter gauge behaves normally at first (e.g. shows small charge rate after start but comes back to zero pretty quickly; remains at zero or very slight positive charge for a while) but after the car's been running 10-20 minutes, the gauge shows a very slight to small discharge. At all times - even from start up - it shows a definite discharge when brake lights or directionals come on. And while I have not tested this extensively to know if it happens every time, I did shut it off and restarted it and the gauge behaved normally again, even though it was hot. I didn't run it long enough to see if it reverted to slight discharge.

Took the panel out and tested the spades for power (engine off, batt still connected) and got about 12v or slightly more on both the black and the black/white ones.

Seems to me that at all times it should not show any discharge when lights, directionals, brake lights come on. Secondly, any thoughts on why it might be behaving differently after it's been running awhile?

Many thanks for your help.

Jack

lvmyvt76

when it is discharging, what rpm is the motor, at idle, it may show a slight discharge depending on WHAT is turned on, like brake lights, heater fan, interior lights, radio etc.
If nothing is turned on, then you may have a problem. Have you checked the out put of alt.? with a volt meter?? This should tell you what is coming out of it, some where around 14 volts, if less you may need to rebuild the alt. IF it is the original, or numbers matching, do not trade it away for a replacement, IMO>

One Owner

Thanks much for your thoughts. Yeah, I'm having pretty much the same phenomenon at all RPMs. And even at idle, all that's on would be brake lights or directionals. The alternator is a new one from Jegs and I think it's fine but will have it checked out again. Where do I test it with a volt meter ... on the single pole with the other grounded? Thanks again!

Alan 71

Hi OO,
Have you looked at the info in the Owner's Manual about what conditions the ammeter indicates? The info might help you understand what you're seeing and when you're seeing it.

"The ammeter indicates the rate at which the battery is being charged or discharged.
The Delco-tron charging system is equipped with a regulator which controls the charge according to battery requirements.
A discharge will be shown if the current demand is more than the Delco-tron output.
With the battery fully charged, the charging rate will be low, thus giving an indication of battery condition."

Regards,
Alan

With the engine not running you can see the ammeter move further to the discharge side as you turn on more lights, for example, indicating the increasing demand being put on the battery.

One Owner

Alan, thanks for your usual great input. I've never had it show a discharge before when running at speed and with practically no load (e.g. lights, etc.). Yes, it should be showing no/little charge and it does do that - for a while. Then it starts showing a slight discharge. I'm wondering if when something gets hot, it's causing the indication to be intermittent or something. Anyway, thanks for your input!!

calwldlife

take a volt reading across the battery so you have a base line.

Alan 71

Hi OO,
" Where do I test it with a volt meter ... on the single pole with the other grounded?"

I think testing the alternators output is a good place to begin.
Red lead on the multi-meter to the red connection on the alternator.
Black lead on the multi-meter to a ground...not the alternator case.

You should see 13.8 to 14.2 volts.
Can you run the car for awhile until you get the condition you're describing and then do another test?
Regards,
Alan

Are you the Original Owner of your 69?

One Owner

Mmmm. Good point. Will do.

One Owner

Another great idea. Thanks Alan.

And, yes, I am the original owner; I was the only pre-schooler to buy a new Corvette that year. I may be getting older but I'm still immature.

dmruschell

I have a car with no voltage or ammeter gauge that was having charging issues. I bought a voltmeter that plugs into the cigarette lighter and used it for diagnostic purposes. It was cheap, and it worked well enough. It might be a good idea to get one to see if there's a problem with the charging system, or if the ammeter gauge is just a little wonky.

One of our C3s with an ammeter always points more towards the charging side than it probably should when the engine is running, even though the charging system is working well with a new battery. It's almost as if it's pointing to where 14V would be on a later model volt gauge.

lvmyvt76

it could be a problem with grounding, have you checked all the factory grounding points?? The big heavy battery cables(from the battery to the frame, & frame to engine) need to be clean, sometimes the one to the battery will be corroded, where you can not see it, the same with the positive cable at the battery & starter. Check all wiring on the alt., especially since you just replaced the alt. A loose wire, or nut, or connector, will make things crazy. Do you have the 2 prong connection on the top??? this when broken or loose will mess things up. In others words, check all connection electrical & check the belt tension, since the alt. was changed.

One Owner

Good thought. Thanks much!

One Owner

Yeah, I had the same thought. Everything looks tight including the two prong connector on the alt and the belt tension seems fine. My bigger fear is that there may be some kind of break or poor connection in the harness (which is original) that heat exacerbates! Thanks for the suggestions.

One Owner

Thanks again for all the feedback.

I did check the alternator and battery, both running and not-running. Got pretty much 14.7 and 12.6 at both respectively. Now showing discharge all the time. Also, my temp gauge was not working on last drive; not sure if I accidentally disconnected it when taking the center gauge panel out (don't think so) or if its failure was due to the same reason as the batt gauge. Also, replaced w/s wiper switch at the top of the center gauge cluster; it opens the wiper door but blades do not work. Have several new grounds: frame to motor mount, battery to frame, 2 frame to exhausts, radio antenna to frame, so I THINK it's properly grounded. Beginning to think it's something with the harness?

Any thoughts? Really appreciate your input.

Alan 71

Hi OO,
In order for the wipers to begin sweeping the wiper motor circuit must be completed by the wiper door limit switch.

This switch prevents the wipers from starting to sweep until the wiper door is fully open.
The switch is mounted on the firewall to the right of the distributor.
An arm and plunger on the wiper door linkage physically push the button on the limit switch to complete the circuit to the wiper motor.

The linkage could need to be adjusted if it's not depressing the button, or the switch may not be working... or not connected properly.
Are you aware of that switch?

You may need to check the operation of the wiper motor if the problem isn't the switch. Do you know if the all the electrical connections at the wiper motor are in place? Is the engine harness grounded at the starter bolt properly?
Regards,
Alan

One Owner

Many thanks, Alan.

I am aware of the switch and it is, indeed, depressed with the wiper door open but, of course, the switch could have failed. I was assuming it had not as the wipers used to work but it's certainly a possibility. Same with wiper motor. I will check all connections and the ground is in place at the starter mounting bolt.

Appreciate the usual good advice!

Jack

Hammerhead Fred

Check the condition of both the field (brown) and sensing (Black w/white tracer) wires that plug into the back of the alternator. They sometimes break right where they enter the two wire plug.

One Owner

I'll take a look. Never would have thought of that! Thanks.

maj75

Did you resolve this issue? My gauge is flakey after having the AC system restored. I know the shop removed the entire dash and I’m certain they messed something up because the gauge worked when I took it in.

One Owner

Not completely resolved BUT I think I'm getting closer.

I discovered one of the grounding straps that connects to each exhaust pipe (at the cross member where the pipes pass through the cross member) was not attached. While I didn't expect it to have an impact on the charging issue, it did cure MOST of the problem when I reconnected it. It now charges normally unless I put on the parking lights (and get a slight discharge) or if I put on the headlights (and get a somewhat larger discharge but not like it was). I saw something the other day about grounding the alternator case and did that as well (to the valve cover bolt). Not sure that it's made any difference. Therefore, I'm assuming that the balance of the issue is ground related but I'm not sure where to find the need for an additional ground.

If your gauge is acting intermittent, it's likely that a ground is not quite tight or something, I would guess. I had some intermittent flakiness as well and I think in retrospect it might have been that cross member grounding strap coming into contact with the exhaust mounting bolt - and sometimes not.

Good luck and let me know how it works out. For what it's worth, I'm just down the road in Weston if we can help in any way.