Electrical: Battery is draining Options

[hi4head]

OK - I got the opossum taken care of and have figured out the windshield washer system, now time for a real problem.

Since the car has been sitting for the past eight years without a battery, I put a fresh battery in about 1-1/2 weeks ago. Friday I noticed that the battery was about dead. I figured that maybe we'd left the cabin light on or something and didn't give it much thought, just hooked up my trickle charger and let the battery recharge.

Yesterday it was about dead again and I started growing suspicious. I figured something was either making contact and it shouldn't be, or I had a bad battery.

I've disconnected that battery and hooked my multimeter up to the positive strap and the ground strap. I would expect that it should show an open circuit, but no, it shows that current can be passing. When I flip the cabin light switch on, it shows no resistance (as expected).

I've left the meter connected and started going through various visible connections and points in the system. (i.e. disconnected each of the connections on the relay board in the engine compartment, removed each of the fuses there and on the fuse board under the steering wheel, disconnected the clock) Nothing that I've done has changed the resistance level shown on the meter.

Anyone have any ideas on how to procede?

Thanks,

Chris

[Hoss]

Chris,

There are plenty of folks on this board who are much more familiar with 914 electrical systems, but I will offer some thoughts in order to understand what you have posted.

1. Battery condition - You mentioned that you have a new battery, and that you fully recharged it. Subsequently it was dead within a short amount of time. I would suspect an internal short or defective battery. A fully charged and new battery would not be drained down that low unless you had a large drain. An operative clock will not pull enough current in that short amount of time to fully drain a battery.

2. Current test - You said that you measured the current between the positive strap and the ground strap. If you are actually trying to measure the circuit current, you should have the DVM in serial. Placing the DVM (set on current settings) from the negative post on one lead and then the other lead on the negative strap will give you the current flow. It is unclear what you think you are measuring based on what you posted.

3. Battery internal resistance - I would check the internal resistance with the battery completely disconnected from the car and compare it to the specifications to help determine if it is bad.

4. Resistance level - I am not sure where you are measuring the resistance, and it probably will not tell you much information. If you determine that the battery is indeed good, then measuring current draw step by step as you tried makes sense to see if you can isolate where the draw is coming from. If you are hunting a fairly significant draw, you could do a quick and dirty by checking the voltage across the battery as well. There will be a voltage drop across the battery that you may be able to see. For example, instead of a baseline 12.75 volts without a load, it might be 12. 5 volts hooked up with something on the circuit drawing a load.

Good luck with the efforts to isolate the problem. I would first suspect the battery since it is new, and there are times a new battery is in fact bad. Assuming you have a good and fully charged battery, conduct the current test with the DVM in series to see what the current draw is originating.

Cheers.

[TimT]

reconnect the hot lead. Then disconnect the ground, and hook up your multimeter between the ground strap and the tub. Set the meter to read amps.

Also make sure everything is off, with everything off you should see 0 amps drawn, If you see a draw, start disconnecting things until you find which circuit is drawing.

this is a start

[lapuwali]

Pull all of the fuses, and measure current across each fuse terminal. That will isolate the circuit that's ON when it shoudln't be. If none of the fuses show current across them, you've isolated it to one of the few unfused circuits (ignition and starter are two I can think of). If you still come up empty, then it's a short somewhere upstream of the fuses, like in the center tunnel or somewhere in the engine bay, or it's some DAPO wiring job that involves a new unfused circuit, or some inline fuse you haven't come across, yet.

[Dr. Roger]

most garages test a battery with a load tester.

harbor freight has a cheapie which i use and can be found HERE

$15.00.

God luck! (IMG:style_emoticons/default/beerchug.gif)

[hi4head]

Thanks for the insights. My apologies if my first post was confusing. Its been a number of years (to put it mildly) since I took my electrical engineering courses and basic electricity. (And even in college - the EE stuff was only the mandatory requirements for us non-EE types.)

Before when I had disconnected the straps from both battery terminals, I think I was essentially performing a continuity test using the ohmeter portion of the multimeter. With infinity being a open circuit, and zero being a closed circuit, I found that I had something in the middle. When I'd flick the cabin lamp to ON, the
ohmeter needle would go from the middle to zero -- a closed or complete circuit.
(Yep - I don't even have a really digital multimeter. I'm using an ol' el cheapo with a needle that I picked up a number of years ago.)

When I reconnected the positive strap and left ground disconnected, I check for amperage going from the ground strap to the negative terminal of the battery. When doing this I get around 18 mA shich tells me that some current, in fact, is draining.

Based upon this, I'm guessing that the problem is not the battery. Although I still could take it back to Advance Auto and have them verify it's still OK.

Oh - do I dispair having electrical problems. I've got new fuel injectors coming this week and thought that I'd be on the road next weekend.

Let me go grill some sausages and then start checking more circuits.

Chris

[swl]

yep. You've got a leak somewhere. Modern cars will have a 'parasitic' load - one that is always there even with the car turned off. Things like keeping your presets on the radio or powering your car alarm. The 914 though really has nothing that should be operating with the switch off. James has got the right plan. Pull the fuses and check with meter in current mode. You can isolate the FI electricals and the ignition with the 12 conductor plug in the back passenger side and the 4 conductor in the back drivers side of the relay board.

[draperjojo]

Pull the fuses one at a time in a dark garage and see if you can locate the ones that arc when you reinstall. If you find one, check that circuit for load.

[Joe Bob]

Fully charge the battery, put a meter at the posts, pull the fuses one by one....ya gets a blip, that's the circuit that being a bad boy.

[hi4head]

Thanks again guys.

I think (hope) that I've got it resolved. At least my meter is now showing no current drain when I check from the ground strap to the negative post. Also, when I do a continuity test, it shows an 'open' circuit and I'm not getting current across each of the fuses. Yee-Haw.

The only thing that I've disconnected was the radio. I find it hard to believe that it would fully drain the battery. I wonder if we had other things on and didn't know it while we were working on the car. I know while we checking the FI system, we were turning over the engine and had the fuel pump and FI system operating to see if the injectors were firing properly. Maybe all of this could have drained the system sufficiently and then I was looking for the needle when the culprit was the haystack.

One of my colleagues at work is an excellent shadetree mechanic (even if all he owns and works on are old Mercedes diesels and diesel tractors). He's also tending to think that Hoss may also be possibly on the right track -- it could be a bad battery.

I've pulled the battery out of the car and have it on the trickle charger and will leave overnight. Let's see what happens then.

Thanks again guys.

Chris