Electrical Question 1964 327/300

[Ed McGettigan]

Over the past year, I've had to replace my battery and alternator once and my voltage regulator 3 or 4 times. I replaced the voltage regulator about 1 month ago because the battery was being overcharged (I checked this by using a voltmeter which went off the scale when the engine was revved above idle). After changing the voltage regulator, the voltmeter read 13.2 volts solid accross the RPM range.

Last night, I went for a drive. At idle, the dash lights would dim slightly but come back bright at higher RPM when driving (it had not been doing this prior - the lights stayed bright all the time). When I got home, I checked with a voltmeter which showed 13.2 volts at idle but when the engine was revved, it would go up to around 14.5 volts and drop back down to 13.2 at idle.

P.S. - my ammeter does not work.

Any thoughts as to what is going on with my electrical system?

[Mike Yager]

Re: Electrical Question 1964 327/300

Ed:

I also have a '64 327/300 and observed similar readings at times. I don't think they are abnormal. I believe a reading between 14 and 14.5 is Ok for proper charging with 14.5 a little on the high side but I don't think its anything to worry about. I think I have observed mine go as high as 14.3 volts.

13.2 is actually a little low. In my opinion, anything below 13 volts is marginal.

I have also observed my lights dimming slightly at idle. I think its normal. I have been running my car like this for years with no problems.

[Wayne K.]

Re: Electrical Question 1964 327/300

Ed,

I have to agree with Mike. I replaced a battery and a regulator because I was told that the old battery was being charged at 14.5 volts which they thought was on the high side. With the new battery and regulator I am still getting 14.5 volts depending on the condition of the charge in the battery and the outside air temp. I haven't had any problems for over a year so just don't think about it. I believe you could take ten different cars that are not having problems and get different readings under various conditions with all ten. My .02.

[Jim T.]

Re: Electrical Question 1964 327/300

In my later model Vettes which have digital readout of voltage, the 14.3-14.5 is normal. the 14.5 after startup and usually pretty much consistant at 14.3. I believe that your lights getting brighter with more rpm on your 64 with an alternator is indication that the grounding of your lights could be improved.

[John Lokay]

Re: Electrical Question 1964 327/300

Jim,
I assume the grounding wires are behind the dash cluster and that each gauge has an indivual ground wire?

[Duke W.]

Re: Electrical Question 1964 327/300

Your slight drop off in voltage at idle indicates that the alternator output is not sufficient to maintain set voltage with the heavy load.

I'm not sure if this is "normal". It depends on the basic alternator output characteristics, pulley drive ratio, and idle speed. If you have added accessories that increase the electrical load, voltage can drop off. As long as you don't spend a lot of time idling 13.2v won't discharge the battery, but likewise, a low battery will receive very little charge at idle.

A common battery failure mode is cell shorting. In this case the battery will draw signficant current from the electrical system, which could cause low idle voltage, but it won't hold a charge very well, so you would likely have starting problems.

Duke

[Jim T.]

Re: Electrical Question 1964 327/300

I no longer own my first Corvette a 64, but I do have the 63 and 64 Corvette shop manuals I bought when I first got the car. I can look for the wiring grounds if you need me to, but Duke Williams can probably help more in this area since his car.

[Ed McGettigan]

Problem Solved!

It turns out my idle speed was too low. I recently lowered it after installing an electronic ignition from 1,000 RPM to 650-700 RPM. I had not really driven it at night so I didn't have much load on the system w/o the lights on.

I bumped the idle speed to around 900 RPM and the dash lights are fine at idle.

Thanks everyone for your input!