VettePekka

I have a '69 Corvette Convertible w/ nom 400cid engine, and MSD 6a.

The problem is that the battery does not hold charge. I am trying to figure out if I have a short somewhere, bad ground or a bad alternator.

The symptoms (in addition to battery dying):

When the car is running at idle rpm (about 600-700 rpm), and I turn on a turn signal, the turn signal will not start blinking, the light just turns on, but does not blink (both the indicator light and the turn signals in front and rear). When I then raise the rpm level, it starts blinking.

When I keep the rpm up, and have my courtesy lights, instrument panel lights and headlights (or some of these) on, they suddenly flash brighter every so often...like every 20 seconds. Once, when I was driving it on the freeway, I measured that the time between these flashes (or sudden brightening) of lights was pretty much exactly 14 seconds...

Also, when I have the car stopped and the rpm @ around 1500 (or anywhere more than at idle), and the turn signal blinking, it looks like the brightness of the courtesy light is blinking a little as well.

When I let my foot off the gas pedal the lights get dimmer.

Also, if I let my foot off the gas just after the lights flash birghter and have the blinker on, the blinker blinks for a few seconds, but as the interior light dim the blinker quits blinking as well.....and will continue blinking if I raise the rpm above idle level again.


What might cause this? Any ideas for troubleshooting & fix would be greatly appreciated.

CHeers,

pete

71406

Sounds like your voltage regulator. I think it was built into the alternator in 1969. On some earlier years it was separate. Try getting a rebuilt one from one of the parts stores. If you have the original alternator you may want to save it and not turn in as a core.

mrvette

IF you have wires on your alt regulator input pair spaced like this..|| i'ts the old style with externam regulator, typically on the firewall somewhere....if it's arranged like this -- in line like that, you are in luck with the later built in electronic regulator......the early one can be converted fairly easy, but no way in hell I can type how to do it....

but over the alternator, MY first step is to check the engine to frame ground.... and battery ground in back negative to frame....

pull all the wires, clean the connections down to bright copper and steel, and shine up the bolts, put new star washers between the wire ends and the steel, and call it a day....then you maybe have to do some Digital Volt Meter work.....but try the simple stuff first....

VettePekka

My application is the latter kind.

How to troubleshoot / determine the condition of the voltage regulator?

Any other ideas for possible causes and solutions?

Thanks in advance,

pete

Flat Black 76

Most parts stores will be able to test your alternator for you if you are unsure how to go about it. I do agree with the previous answers. I just dealt with a similar problem on a Yamaha bike (sounds stupid, I know, but the principles are the same), no blinking, dim lights, dying battery - replaced the rectifier/regulator and like magic ALL problems solved. Just my 2 cents.

StickShiftCorvette

First charge your battery and confirm that the blinkers and all of your electrical systems work without the engine running. Depending upon the number of things you run, you should see 20 to 40 amps of discharge. If your systems don't work with the engine off, you need to figure out what's wrong. If things don't work right disconnect the alternator electrically and see that all the systems work.

Everything should work with the engine off. If it doesn't, its not the alternator.

VettePekka

Took the battery out of the car, and charged it up a couple of days ago...it has been holding the charge very well.

So, tonight I am going to put the battery back in and check things out w/o having the engine running.

cheers,

pete

VettePekka

I put the battery back in and tested the turn signals w/o starting the car. They do blink, however at somewhat slow pace; at slower pace than if I have the car running and raise the rpm to above idle.

That leads me to the next question; does it appear that the alternator would be the culprit for making the lights flash / brighten, and cause the battery to die (not to charge)?

MikeMc71

The alternator and regulator work together to charge the battery, since they are a packaged unit, take the alternator down to an auto parts store and have it checked.

Tim_Ko

If you think you have a short somewhere that is causing the battery to drain, you'll need a multimeter to measure it. Take off the cable off the neg side of the battery and connect the multi-meter in the DC amp mode between the Neg battery post and the cable. If you don't have a multimeter, connect the positive side of the battery, and touch the cable to the neg side and see if you get a spark. If you get much of a spark, you have current flowing. Pull the fuse to the instruments (clock) and see if you still get a spark. Pull the fuses one at a time and see if you can find out which circuit is drawing current. That will help you to narrow it down.

MikeMc71

And pray to the Almighty that its not more than a few milliamps draw....or you'll trash your meter!

This is gonna get good, I can tell............

RAGTOP75

I am having battery drain also. My multimeter reads 12.68 volts across the neg cable and battery. I removed all of the fuses and nothing changes. What next?

Tim_Ko

Wait a minute!!! There are three measurements; voltage (V), current (I measured in amps) and ohms (R for resistance).

The + side of the battery is +12V. The - side of the battery is 0V (GROUND). If you take the ground cable off the - side of the battery ... then the circuit is OPENED. Current will not flow across the air gap.

Set the multimeter in the DC AMPS mode (not the DC voltage mode) and place one side of the meter on the NEG post of the battery and the other side on the BATTERY CABLE CONNECTOR. Now the circuit is complete ... through the meter and current will flow. Set the meter to the highest setting so you don't peg the meter. And, see what current is flowing. [[my car had 3.5ma flowing and the battery drained ever 3-4 days. if I drove it every day ... no problem.]]

Since you took the fuses out ... measure how many amps with no fuses ... and add the fuses one at a time until you see the some kind of current flowing. Then you will know which circuit has the SHORT.

SIDE NOTE: If you have the neg cable connected to the - side of the battery and there is corrosion in there between the connector and the post ... the corrosion acts as an insulator.

Good luck, let us know what you find.

Boofers

The battery needs higher than 12V to charge it. With the engine running above 1500RPM the alternator should put out between 13.5 to 15 volts (you will measure this across you battery terminals). With the engine below 1000RPM the alternator is turning slower and generally will only put out 12V. This is why on our cars the lights generally dim when the engine idles.

If you are not getting above 13.5V with the engine over 1500RPM then your alternator probably needs fixing/replacement.

VettePekka

ok, some more test results are in....

Took the car to the near-by Napa, and they measured 12.9 volts at 1500 rpm, and just under 12v at idle. So that would kinda indicate that the alternator is the problem. But would that explain the sudden flashing / brightening of lights every 20 seconds or so...?

I then took the alternator out and it was bench tested at Napa.....and the result was 14.5 volts....why the difference?

Someone suggested that the alternator brackets do not provide a solid enough ground...could that be my problem.

Anyways, what I had left out from my original explanation is that I also have electric fan and fuel pump. Would those set-ups already require an upgraded alt. The current one is a 63amp 10-SI. I am thinking about 94amp 12-SI.

Any thoughts?

VettePekka

bump

jdp6000

Definitely. Depends on the draw of the fans. Depends on the fuel pump. Easy test.

Disconnect the fans for a minute or so...don't want to over heat your car. Does the problem go away? How many amps does yours draw? How is it connected? what type size fuse are you running?

What type of fue pump do you have? does it only turn on periodically to charge the system or does it stay on constantly?

Jim

Boofers

If you demand more current than the alternator is capable of providing then the voltage will drop.

VettePekka

Got my electrical problem(s) solved. First off, I replaced the old 63 amp 10-SI alternator with a 94 amp 12-SI.

Secondly, I made sure that the alt case is well grounded....dedicated ground cable directly to the frame.

Thirdly, replaced the flasher.

Life is good again.

Thank y'all for help!

Cheers,

pete

Boofers