Jim Shea

I found that the battery in my 75 was dead today. The battery was fairly new (it is only a year and a half old.) I connected my charger to it and it settled in at about a 2 to 3 amp charge. I left it on for a couple hours and went out to try and start it. I disconnected the charger and found everything dead as a doornail! I reconnected the charger and now it pegs at 6 amps and kicks off. I thought for sure that I had a dead short in the battery but when I removed the battery from the car I find that it takes a charge!

I know that this has been discussed recently as to how to find the source of a continuing battery drain. Connect a meter to the battery and disconnect various fuses until you find the circuit that has the current flow. I haven't had time to try that approach. There was also mention made of the rear compartment light staying on and also a defective voltage regulator on the alternator.

One question is how do you determine that your voltage regulator is bad in the first place? Does my description of the problem give anyone any ideas as to what is wrong? Your help is appreciated.

Captain Morgan

Pull the voltage regulator and take it into a parts store and they'll test it for you. Not sure if the voltage regulator is inside the alternator or not as I haven't had to work on that part of the vette (yet). If it's an internal regulator, pull the alternator and take it in. However, I'd chase down the cause of the drain, I doubt it's the regulator or I would think you would notice the volt meter bouncing around or playing dead while you were driving.

Clink69

I had mentioned in my previous post that the Diodes in the alternator could be bad. These are used to convert AC to DC when configured in a bridge. basically to eliminate these just disconnect the alternator while watching current. But if you have a drain like you described it could also be in the starter solenoid shorting. Also be careful when measuring current as it is quite easy to fry your meter. :flag

daily_driver

usually if the starter does indeed have a short it gets hot....

when u havent run the car for 10 seconds and the starter is really hot that is a dead giveaway.....

try it out...

ED DINAPOLI

Jim,
To check to see if your regulator is working; Run the engine and check the voltage at the battery It should be between 13.5-14.5volts. If the voltage is lower than 13 v your regulator is suspect.
To find the drain you will need to do the circuit by circuit check as you mentioned.
Ed

Biker

Jim, I had a battery drain problem on my '81. I installed a cut-off switch at the battery, which solved the problem.

KenSny

I had a problem similar to this when I first got the car. The battery +cable was shorting near where it disappears past the tranny. Seems to me that since you cannot even start the car (assumed from what you are saying) then you have a direct short someplace. Especially since you can charge the battery and leave it set (all hooked up in the car) and it's dead again.

On the other hand. I have had batteries that seem to take a charge, but will not hold them very long. You might want to take the battery back to where you got it and have them test it.


[Modified by KenSny, 9:04 AM 10/31/2001]

Jim Shea

I installed my freshly charged battery which read 12.5 volts this morning.
I have taken all the fuses out and disconnected all the connectors from the fuse block. I also disconnected the red wires from the alternator.

With all this, if I just connect the positive cable to the battery and jump across from the negative cable to the battery, I still read 12.5 volts. It seems to me that I should be reading zero unless there is a short somewhere between the positive cable before it gets to the fuse block. Looking at a wiring schematic, I see that the positive cable goes directly to the starter solenoid. It also seems to go to the horn relay and key warning buzzer without going through the fuse block as well.

I am also confused in that I don't know what scale to read on my volt meter to try to figure the current draw. Since I am a mechanical engineer, maybe I should have studied harder in my EE classes. I have both a digital and an analog volt meter. I assume the analog should be set at 150mA DC. The digital has 2000mDCA and 200mDCA settings. I couldn't get any kind of constant reading while trying to remove the fuses.

The meter should be in series between the positive or the negative cable and the battery?

Jim Shea

ttt

daily_driver

indeed when measuring current draw, make sure u hook up the meter probes correctly to measure current...

you then hook the positive (or negative) cable to the DVM then to the battery....... (thats series of course....)

another way to do it would be to disconnect the negative and positive cables and do a continuity test (most DVM's have this...) between the positive and negative cables....

then pulling fuses should eliminate sub circuits and tell you where on the schematic your going bad...


i myself would use the continuity test with a beep function so i dont even have to look at anything...

hard wire it up with alligator clips and just pull and put in fuses and see if you get lucky and find the problem....

Captain Morgan

You are correct about the meter needing to be in series with the battery - it's best to use the negative cable. It might also help to have some clips rather than just the probes or ,even better, have a friend pull fuses while you watch the meter. You can disconnect the key buzzer itself, it should be under the driver's side dash and I believe it's bolted the the firewall. Mine has a green and orange wire on it, maybe a third wire too but I can't remember off the top of my head. That's where my drain was coming from. The buzzer would only sound when it was supposed to but it would drain the battery within three days if I didn't drive the vette. Good luck, let us know if you need any more help.

BubbaJJ

I'm no elecrial expert but it seems to me that if you have a direct short anywhere it would burst into flames and melt wires. It would either have to be shorted somewhere inside something with a lot of resistance or something is stuck on. My 75 had the same problem until i took the bulb out of the storage compartment in the middle. The cover was warped just enough so that the light would'nt go off. After a couple of days, dead battery. After a week, really dead. The way you can check for a drain is to disconnect the terminal, get inside so that all the lights and buzzers are off and then drag the terminal across the post on the battery. If you get small sparks you have a drain somewhere. With the doors closed and everything off, the only drain you should have is the power wire to the clock and any memory wires to the stereo. You can disconect an aftermarket stereo pretty quick. I'm not sure how hard it would be to disconnect the clock. It may have it's own fuse, I haven't looked. While your doing this, open the center compartment and hold the button down on the light to make sure that circuit is dead. Good luck. Oh, be careful, you could ignite any hydrogen gas that may be lying about. use a meter if you have it or ventilate well.

2nspire

I have just went thru the ' battery drain ' process. My battery was dead after 1 day. I put my volt meter on 10 amp, disconnected the neg battery cable, and closed the door so delay interior light went off. Put neg prong on neg cable and pos prong on neg battery post. 2.99 amp reading on voltmeter. Then I pulled fuses 1 at a time. Still had 2.99 reading. I had also just changed starters and also hooked up rad fans power supply to starter. I then took off all wires to starter and then put them on 1 at a time. BINGO! It turns out that there was a wire that had the right connection on the end to fit on starter bolt that shouldn,t have been there. I had forgot about it. That wire was also a live wire. End of battery drain. Bad part is that because I had drained and charged the battery so many times that my battery was now no good so new battery now. This has been my experience this past week. Now with the new fans and bad alt. belt alignment I just cooked my alt. tonight. So I guess it's a good time for a 100 amp alt. I'm talking my car out tomorrow to break in the new engine so I'll take a few batteries with me and when one runs out, I'll have to change batteries cuz I ain't gonna wait for a new alt. Good luck to you on your battery drain problem.

Barry's70LT1

Hi Jim...
Several years ago my neighbour had a power drain in his Chevelle.
He went through all the same great suggestions that have been posted,
however it continued to have a 500ma draw.
One Saturday we started checking everything.
To make a long story short, it was one of the interior light door switches.
It had corroded and became "resistive" and was passing current.

This is not likely what you have, however check for corroded contacts
that possibly could be leaking power to ground.

Jim Shea

Things just seem to go from bad to worse. With my DVM set at 10 amps, when I try to touch the probes between the negative cable and the negative battery terminal, I get a hellaesish :reddevil spark. So I am afraid of frying my DVM (or burning the car and house up). This is with all the fuses pulled and the positive leads disconnected at the alternator. I'm concerned that there is a dead short. And my thinking is that it must be between the battery and the starter. It's time to jack the car up and try to check the cables under the car. Next, I should probably pull the starter solenoid? Or the whole starter?

daily_driver

to answer the dead short question just disconnect both cables from battery and do a continuity test between the negative and positive cable..


if it beeps / lights then youve got a short.

daily_driver

i would pull the whole starter.....

ive had way too many starters develop shorts....

one had a short so bad that the thing got so hot you couldnt even touch it...

kinda a dead giveaway there...

Jim Shea

I have a dead short between the positive and negative cables (same reading between cables as touching my probes together). So now the question is where?

daily_driver

a very good start would be to yank the cables off the starter and test between the negative and positive again...

(make sure the cables arent touching the body... let em hang...)

thatll rule out the starter without completely yankin it...

obviously if you get no beep /light then the problem is in the starter...

otherwise its time to break out the wiring diagrams and narrow things down!!

daily_driver

duhhh

i should say....

yank the starter cables off and do a continuity check between negative cable and a always on lead elsewhere (not positive cable...)

thatll tell you if the short is elsewhere...

if you have continuity between the negative cable and positive cable when you disconnected the cables off the starter then the positive cable is touching the frame in the tunnel.... and that positive cable is a major PITA to change....