bronto

Intended to drive the '79 928 to work this morning, but the battery was dead. Turning the key made the needles move slightly, but the starter motor didn't even click. The clock (which previously kept perfect time) was stopped at 3:15.

The car has been sitting since Friday night or Saturday (not sure if I drove it on Sat). Brand new battery. I don't believe I left anything on, although I did leave the fog light button depressed; but the lights themselves weren't turned on.

When I first got the car home last month, I took it to the mechanic, where it sat for 3 weeks or so. They mentioned that the (very old) battery was dead too. Previous to that, I had driven it daily for a couple of weeks with no problem at all. For a couple of weeks since getting the car back from the mechanic and installing a new battery, there also was no problem. The seller mentioned that he needed to recharge the battery before delivering it as well, but it also had been sitting for several weeks.

So it appears to me that there is a slow draw on the battery that's killing it. Surely the clock wouldn't be doing this(?). Are there other common things I should be looking for that might be doing this?

Thanks.

Colin Emerson

Same thing is happening to me right now, just went and put a brand new battery in, and go to start it and nothing. I think something funny might be going on at the positive terminal, I noticed after I put the new battery in that my stereo has no power, in fact one time, it cut out completely then came back on. Last time it ran I had no juice to the stereo. The car runs perfect when started from an auxilliary battery, it will even start up after I turn it off, but leave it for a day or two and no go. Kind of sucks because I am nervous about tkaing it anywhere in case this happens again.

the flyin' scotsman

Had a similar issue of battery being drawn down and it was the rear tailgate light; it was in the 'on' position. Reckon my golf bag hit it.

A simple check to make sure all the interior lights go out with the doors and tailgate closed; remember they have 3 positions; off, on with door/tailgate open and on all the time.

Colin, sounds as if you have a diiferent problem; how's your ground cables?

bronto

Actually, I had just been checking my interior lights last week, so I've already been watching that carefully. I'm certain that the two "above head" lights were off. Maybe there's one I'm not watching? I was watching the one at the windshield, and the one on the top of the hatch. Both of those are set to turn on and off when the drivers or passenger door open. I hadn't seen a light that goes on when the hatch is open. If I have one, it's buned out and I don't know where it is.

Where is teh switch for the "rear tailgate light"? Do you mean the hatch?

symantics...

SharkSkin

Charge that battery back up ASAP. Nothing will permanently kill a battery faster than leaving it discharged for more than a few hours.

The switch for the interior lights when opening the hatch is at the bottom of the latch receiver. Pull off the tool cover and it should be right there.

Alan

Its certainly possible you are draining the battery - but its also possible the battery is just about dead.

When batteries go bad there isn't much you can do to resurrect them.

The only way to know is to take it into a store that has a good tester. You may need to leave it to be charged (charging alone may tell them its dead) but then is should be tested on a load tester (a real one - it will be big with a large fan) not a puny handheld tester. They will test voltage first - if it reads below 12v your battery is dead - get a new one (regardless of what they say- some monkeys have tried to tell me that my 10V reading freshly charged battery was still good...!).

Anyway if the voltage is good they will lload it with a big load and see how much current it can put out this is the real life test to see if it has a hope of starting your car... I'm guessing NOT due to the multiple full discharge cycles and standing time...

It could just be you need a nice new fresh battery.

To test for leakage you really need an ammeter in series with a good battery (but very carefully)... check the many previous discussion of this.

Alan

macreel

bronto... my 'favorite' gotcha... check the red door edge
safety lights and the door-mounted courtesy lights.
Sometimes they come on when the door is slammed
shut. In the daytime they're hard to notice.

Does your '79 have all those ?

G'luck.

bronto

Yes, this is a brand new battery.

bronto

I don't believe mine has those.

Dennis Wilson

May want to check the connections on the overhead light (above rearview mirror). The positive connector on them have been known to come loose and contact the roof.

Dennis

the flyin' scotsman

whatever, the thing that opens in the back.

My car has 5 inside lights; all of them can be seperately position as mentoined............check them all if you have 'em.

bronto

Interesting. Thanks for the idea. Does it matter that the light you mention does, in fact, work? I would think that if this were loose, the light wouldn't work.

My 928 only has 2 interior lights that I can see, to answer the other questions.

SharkSkin

It can still be a partial short, not enough to kill the light but enough to draw power.

The wiring is pretty simple on your car, very few fancy latching relays/circuits compared to later cars. Here's a simple, minimum-tech test. First, switch off the interior lights so they don't turn on with the door open(better yet, pull the bulbs). Make sure all electrical systems are turned off -- parking lights, etc. Then pull the ground wire off. Connect a brake light bulb between the ground wire and ground post. You can get a socket for a brake light bulb at the parts store, and some alligator clips to connect the wires with. If the bulb lights up, you have a current draw somewhere. Pull fuses(carefully noting their original position so you don't mix them up) until the light bulb goes out. The last fuse is your suspect circuit.

bronto

That's a great idea. I already have a circuit tester with a bulb in the handle. The clock is certainly going to affect this too though, won't it? Is is easy to pull or disable the clock?

SharkSkin

Clock draws so little power I wouldn't worry about it.