Korwen

Rennlisters,

Ever since I've owned this car it's had a severe battery draw, to the tune of 2.2 amps with everything off. Needless to say if I park anywhere for more than 6-8 hours, I unplug it or else it's dead. I've been taking some of the first steps towards trying to find it, and I've got what I think are some unusual results, and I'm hoping you guys can tell me where to look next. As mentioned in my sig, it is a 1982 model.

First I hooked up the multimeter on one end of the grounding strap, and the other end on a ground, making it part of the circuit, and it read 2.2 amps. I then pulled every single fuse out of the fuse box, and it's at 2.2 amps still. I found that some of the fuses weren't the correct ones, so I replaced them all with the correct fuses according to the fuse diagram on 928 Specialist's site, still 2.2amps.

Since I figured it's pulling 2.2 amps with all the fuses out, that eliminates most small draws. None of the interior lights work and I've got a weird short in the hi-beam lights where if I turn the high-beams on, the right side of the dash (tach, voltmeter, oil pressure, blue light) all go dead. I don't think those are related to the draw however since it is so severe, and those are all fused circuits and it was still drawing with all the fuses out.

Now to the wires that don't go through the fuse panel. I just now decided to pull the big red wire off the alternator. I did this, and all of a sudden my draw jumped up to almost 5.6amps! (5.58 technically) I then decided just for grins to pull out all the fuses again, and no change.

So here I am. With the alternator plugged in it draws 2.2amps regardless of the fuses. With the alt unplugged it draws 5.6amps regardless of the fuses.

So, where to next? It seems logically like it would be somewhere in that thick red wire that goes to the alternator and to somewhere else, but I don't know. I'm hoping you guys can give me some insight on where to look next before I continue to disconnect everything.

Edit: Should be noted that every time before I mess with something like the alternator I have the battery completely unplugged, and am wearing gloves with rubber on the underside of the hands. I don't feel like internal electrical burns.

WallyP

The alternator draw is odd. Try disconnecting both the red wire and the smaller exciter wire and see if the draw changes. Be VERY careful - the red wire is a direct, unfused connection to the positive battery terminal, and would be a major short circuit, with major harness damage if it touches the chassis.

You need to fix the interior lights - the door switches control several items on the car. Get the switches working correctly ASAP.

Check for any aftermarket alarm systems or audio systems, especially amps.

Lizard928

I would recommend that you remove the jump post from the car and seperat the connection rings. Read your draw then. You should loose ALL draw, If you dont then the power can only be going through the altenator, starter, or a couple of others which have their own wires off the + post. I think the fuel pump is one of them.

You should also pop out each relay and watch for the amps to drop.

tailpipe

it could be the diods in your alternator they may have an internal short I have had two go bad like that on me both in a 79 model I think from being oil soaked, you can buy a new diod pack mine was less than $100 just need to resolder the wires inside the rest is just a few screws. I had the alt checked and they still charged fine just the diods were draining the battery like yours when it was shut off. I did like you also and also disconnected the batt when I wasn't using it that worked for about a year untill the diods finally shorted out completely and the batt went dead as I was driving. Luckally I wasn't to far from home. Your symptoms sounds just like mine maybe try a known good alt on your car to check
good luck


Paul

VehiGAZ

I may be mistaken, but I was under the impression that you cannot measure current accurately with the multimeter probes. The only reliable way to do it is the use an ammeter probe, which is a circular device you put around a wire to measure how much current is running through it.

While you certainly have a current draw, you may be chasing ghosts with your measurement technique.

Also, I think you are wrong to assume that your headlight and interior lighting issues are unrelated to the draw... my guess is that they are the cause of the draw. Why? Because your draw is not fused, which suggests there it is caused by a short to ground. Also, it seems that many electrical circuits in a 928 are tied in to the interior lighting.

Alan, the 928 electrical guru, is the one to consult. He always seems to have people start with fixing their interior lighting first.

Good luck!

the flyin' scotsman

The method you are using to measure current is correct but I'd double check the settings on the DMM as well as the position of the leads...........there's different positions for current measurements.

The readings you have are very high.

VehiGAZ

That's why I was doubtin' - a 2.2 amp draw would drain the battery pretty quick.

Korwen

Right now I'm looking at about 8 hours from turning it off to a flat battery.

JoeTaylor

Hi Korwen,

I dont know if this applies, but the PO of my 1988 S4 had the shop that serviced his car add a relay back in the battery compartment.

When I asked the shop owner about it, he said they installed it to disconnect power to the ECU when the car was turned off. The PO didn't drive the car much and the power draw from the ECU continued when the car was off. He went through a couple of batteries until that fix was applied.

I dont have any more details about it. The shop owner did show me the relay back in the battery box which basically dropped the connection to the ECU when the car was turned off.

I hope this helps.

VTY,
Joe

soontobered84

Korwen,
When you say the interior lights do not work, are you including the door safety lights? ( the red ones in the end of the door) These are usually really corroded to the point that you may have a short or a ground or something like that. I am no electrical guru so I would have no idea why you get such a drain when you disconnect your alternator. Check what the guys have posted above, but also check those door safety lights. Normal working ones will kill a battery overnight if they are on.
Good Luck!

Korwen

Interestingly enough, these lights do work, also my door switches aren't stuck in.

the flyin' scotsman

If your truly drawing 2.2amps most of the cars wiring would be burnt.

Did you disconnect the starter then measure?

Korwen

Not yet, that and the jump post are next on my to-do list - if I would ever get out of work! darn overtime.

However, if your assessment about 2.2amps burning wiring, that might explain a couple of the burnt wires on the printed circuit for my gauges. I could also attribute sticking higher amp fuses where they should be in there too, another PO screw up I discovered while troubleshooting this.

Korwen

PROGRESS!

Sort of...

So tonight I unplugged the starter, removed the jump post, unplugged the 16 pin connector and plugged the battery back in, and what once read 5.58, now reads -0.03.

So now I know if I disconnect everything in the car, there's no drain, which eliminates...
Crap, nothing, I just know unplugging everything works, but it's progress. So here's where I ask for the next bit of advice on this. Do I plug back in the starter, measure it, then plug back in the jump post and measure it? If I do this then I know it's somewhere pertaining to the jump post, or do I plug back in the alternator, the starter, the 16-pin connector and leave the jump post undone, and then try it further isolating the problem? I'm not too knowledgeable about troubleshooting electrics (So I'll get a lot of practice with a 928!) so I'm still needing some advice, however I do appreciate all the help, and I'll keep posting my progress in case someone else can be helped too!

JoeTaylor

Hi Korwen,

Troubleshooting

Now that you have eliminated the drain, the troubleshooting begins by connecting only one thing at a time and disconnecting it to determine where the drain is coming from.

Say you have 5 connections to make and break and connection #4 has the "drain" on it, then you have eliminated connections #1, #2, #3 and #5.

Now, connect only #4 and "swim upstream".. meaning go up the wiring loom and find out what #4 connects to.. repeat the procedure if there are multiple connections.

Eventually, you will find or narrow down where the problem is.

Source of the Problem

It could be something as simple as a frayed wire touching ground, a broken fixture or broken connector/insulator, etc. Most electrical problems are like that on a system that designed correctly and worked ok to begin with.

There is the other factor that a PO or his service person ran some unnoted wiring in the car, something to watch for.

But if you follow the proceedure, you will find it!

I hope this helps.

VTY,
Joe Taylor