Eliminater2

I am a newby to Corvette Forum but I need help. I am restoring a 71 coupe, all new wiring harness, new switches, fuses, the whole nine yards. Everything works but with every thing off it drains my new battery overnite. Any suggestions?

Kevins77

I would do is check to see if its grounding out - Are you handy with a multimeter? Its a really simple process, just takes a lot of time.
First thing I would do is see how many ohms you are pulling at the battery with everything hooked up and the key off. That will tell you quite a bit.

fastcw

I worked on a battery drain problem for days. Finally found that the glove box compartment switch was not being fully depressed, and the light was on, but couldn't be seen since the compartment door was closed.

You need to connect an ammeter in series with one of the battery leads, and get a reading on the drain current.

Then you can pull one fuse at a time, while looking for the drain to go away. That will get you on the right circuit to look at.

I always pull the drivers seat when I have to work in the fuse block area, it will save you a lot of time in the long run.

larryg3

that is the best way pul one fuse at a time until you find the right circuit.

roger3

I had the same problem and it was my glove box light not turning off when I closed the lid.

I would check that first.

thoyer

Use a DVM, digital volt meter, and set it to read DC Amps. On some meters you need to move the test leads to different inputs on the meter. Then disconnect the positive side of the battery. Put the red lead on the positive battery terminal and the black lead to the cable. With everything off you should read zero current. If you do read current then as suggested above, pull one fuse at a time to locate the offending circuit.

Good luck,
Tom

hooperdoski

Bad alternator diodes will also drain the battery, but I've never seem them drain the battery overnight.

Your battery may be shorting out as well. A hydrometer, which is cheap and simple to use, will tell the story on that one right away.

Also, like Tom said, you need a digital multimeter. I always check current draw by checking milliamp draw through the negative post although the battery is draining so fast that Tom's and other's suggestion at checking current voltage at the positive post will work and then the fuse pulling should get you there if it's not the battery or alternator diodes.

Good luck.

hooperdoski

I left the computer and thought about your battery drain again. If your clock is working then you're going to read 12 volts with Tom's suggestion. You need to measure current flow. You can do that by getting a digital multimeter and reading the instructions on measuring current flow.

Both the hydrometer and digital multimeter aren't that expensive and are good and necessary tools to have when you're chasing down electrical problems.

JMS71VETTE

Best advice on checking out circuits for drain.

thoyer

Actually you will read the current draw of the clock which should be negligible. By removing the positive wire and connecting the DVM in line with it as I suggested, you will read current draw (assuming you have the meter set to read current).

To read voltage you would connect the meter from the positive terminal to ground. for the purposes of diagnosing this problem, voltage measurements won't help.

Tom

hooperdoski

JMS71VETTE is right. He is basically saying the same as I am. Drain and current flow or current draw are the samething. You just need the multimeter and its instructions on measuring current.

As for the fuse pulls it will show a bad circuit, but will not show a bad battery (use hydrometer) or bad alternator diode/s. However, if the fuse pulls don't show a bad circuit or eliminate the draw and the battery is good then the alternator should be checked.

As for testing the alternator, I use to diassemble the alternator and pull the diodes out to check them, but I think some shops can test it for bad diodes.

When you do the fuse pull make sure the courtesy light/overhead light is not on. I have forgot that many times.

Eliminater2

Thanks for the replies. I now have a starting point. I will let you know how it turns out.

my 76 ray

An easy and cheap way to check the battery is to charge it, remove it from the charger and let it set for a day or so. Then hook it up and if it's dead, you know the problem.

captgary

Since you put new harnesses in, check the wires going to the alternator plug they may be reversed. A easy way to check is after everything has cooled down put your hand on the alternator and see if it is a little warmer around the plug area. If it is wires are reversed.
Had this prob myself PO had it wired wrong, I think thats why he sold it, he could not fix it the good part is I got a new battery, alternator and battery wires and belt.

Eliminater2

Turned out to be bad alternater and bad air conditioner relay. Thanks to everyone for your help.

Peterbuilt

Glad you figured it out since for me solving electrical problems has always been difficult.
How did you find out the a/c relay was bad?

Eliminater2

I called the company in Calif. that made the wiring harness. The guy there spent about 2 hours on the phone with me running test on Tues. then again on Wed. He narrowed it down to the alt. and air conition relay. Super people to deal with.