Battery Drain........Fuse#24

[Penrod]

So I had a pretty serious battery drain, would be dead if it sat overnight.

I used a multimeter(set on 10Amps), in series. When first hooked up it would read 1.25A, within 10 seconds, and a click at the fuse box it would read 0.53A. Still a very large drain, after pulling the fuses I found the culprit to be Fuse #24, which controls, interior lights, diagnostic computer and something else. BTW the reading dropped immediately to 0.11A when pulling this fuse.

To the point, I can let my car sit for extended time now, however I would really like the dash computer to work. I am assuming this has something to do with my interior lights.......any idea where to start? I currently have all the lights in the off position....where is the problem? The only way around this so far is to pull the fuse everytime my car sits for more than 12 hours, then plug it back in when I want to drive with the computer working

Thanks

[rhjames]

Holy Crap.....

this is the same thing my 928 has done.

disconnected every thing that operates on that circuit, put the fuse back in, and it still kills the battery overnight.

I figure it's in the wiring somewhere, but haven't got into tearing the upholstery out yet......

when you trace yours down, please let me know!

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[Penrod]

I am guessing that it is probably a loose wire at one of the interior lights, I will soon start taking those apart. As for the computer there is not much I can do about that....it only makes sense that it should be the simpler (a loose wire) fix. At least I can drive it now, pull fuse, replace fuse and start her back up the next day.

I will let you know if it turns out to be a light switch

[Danglerb]

+1 to what Jimmy said, shorts in the wires around the overhead switches are common.

Drains are pains, on my 84 parts car I pull the ground to the battery every time I park it. I'm looking forward to the last time I do it too.

[rhjames]

took all interior lights out (including the door lights)---wrapped the wires in tape, disconnected the cigar lighter, disconnected the radio, disconnected the speaker wires, disconnected the wiring harnesses from car to doors.........went thru all of this and still a hot fuse and battery dead overnight....

try all of this, step by step as I did, and then tell me what you find......I know of nothing else on the circuit that operates that fuse in my '80 Euro....at least that's what the wiring schematic says. your's is perhaps different, but that's where I'm at with mine.....

have not stripped the interior to check the wiring from fuse box to where-ever yet.....that could be next, but unlikely in the near future.

try again?


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[Penrod]

Thanks for the responses guys!
I am hoping it is just a loose wire grounded out, will get to it this weekend.
My car is an 89 so when I pull that fuse I lose the diagnostic computer, but it is still very driveable. However, messing around in her last night I noticed that the fuel gauge reads empty and the oil pressure gauge reads very low. The low oil pressure kind of panicked me at first, checked oil..okay, put fuse back in, oil pressure sits at 3 idling,5 on the throttle, and the fuel gauge reads what it should.

[Danglerb]

Lets just say the average old 928 has more than one path from the positive side of the battery to the ground. Wallly's ground cleaning should be on everybody's list if they haven't done it recently.

http://members.rennlist.com/jerdmann/electrical.htm#anchor_2

[mdarney]

What is the engine diagnostic computer? My wiring diagram shows interior lights only in the schematic. I have a drain as well but have yet to find the culprit. I just bought the car 2 weeks ago and just got a multimeter today, along with a new battery. How did you check the voltage did you pull the positive and put the meter between the battery positive and the main cable or is there another way to check voltage use with the key off. i have not yet checked each fuse yet. I have removed feet of wire associated with an aftermarket alarm system and radar detectors put in by previous owners. -Mark


1985 5 speed 928

[Danglerb]

Diagnostic computer is warning lights stuff I think.

Meter use, between I would call "in series" and thats for measuring current, across I would call "in parallel" and thats for voltage.

Be careful measuring current, many meters for electronic work have very low limits of current that can safely go through them. Most have a fuse, but it might be a pain to replace. Read the manual that came with the meter.

Key off, battery connected normally, you ground the negative probe of the meter to the chassis, and go poking around with the plus probe looking for voltage.

I pull the battery ground connection, old habit, and that is where I would measure the key off drain (current so meter goes between battery and battery cable.

Be careful, 12v isn't going to shock you, but a 928 battery is a monster and high current through a shorted wire can burn both you and the wire. Frying the loom, all the wires behind the relay panel, is very bad.

[Penrod]

mdarney

My car is an 1989, so it comes with the digital dash/diagnostic computer. Just gives you digital warnings on top of your gauges that you already have. It also displays, 2 trip meters, outside temperature, instant fuel consumption, average fuel consumption, average speed, current speed and all the warning lights.

You need to put your meter in series between the positive post on the battery and the positive cable. Make sure your meter can handle at least a couple of Amps, anything like 200-500mA and you will blow the fuse almost immediately(just like Danglerb said). Basically if your car's battery is going dead overnight you should have a fairly hefty drain...ie in excess of 1 amp. From what I have been told a couple hundred mA's will not drain your battery overnight

Once you know what the current drain is.....jimmyt123 quoted around 60mA as being about normal for the car, I would bet you will see over an amp. Then get a helper to read the meter for you as you pull fuses from the passenger side.

In my case it was fuse 24: interior lights(the most likely suspect) and the diagnostic computer. First easy step is check those interior lights to make sure nothing is loose.
I am thinking I might replace all the fuses.....as I was pulling them 2 of them basically tore themselves apart. I also noted that they looked quite dark, almost dirty, I am pulling them all and replacing them with new. Who knows how old some of them are and how intact they really are.........

[mdarney]

Penrod,

Can you simply put your meter across the removed fuse terminal and see which one has power to it with the key off? Thank you for the advice so far, keep me posted what you find. My interior lights do not function with the door switch but work otherwise, so I may have a short in the switch.

[Penrod]

mdarney

I am not sure if you can do it that way, anyone else know? It might be hard to do with the meter probes because it is pretty small in there.

The way I described should definitely find the drain though. My wife helped me and she just kept reading the meter out loud and as soon as I got to that fuse....bingo!!!! Tested it a few times by re-inserting the fuse drain goes up, remove it comes right down. Make sure you test all of the fuses in case you have more than one cirsuit draining.

I will be looking at my interior lights this weekend, does anyone know if the light under the hood is tied to that fuse..the problem could even be there.

[m21sniper]

I installed a moroso heavy-duty racing grade battery disconnect switch (30 bucks).

Problem solved.

[rhjames]

it goes along with his ricer wheel spacers-----ha, ha, ha.....



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[m21sniper]

Originally posted by jimmyt123
You didn't solve the problem, you merely disguised the symptom.

As long as it suits you and you're happy with it.

Battery doesnt drain anymore: Problem solved- permanently for under 30 bucks. (it also offers nice fire protection and anti-theft protection as an added side bonus)

RH what is your problem? I use custom made hub-centric wheel spacers, not cheap or rice at all.

Dont you have some garbage to haul or something?

[Alan in AZ]

The correct current draw if everything is working right is about 15mA.

About 300-500mA is the approx level of relay coil currents - so I'd suspect this level of draw means something is staying on. If your interior lights don't trigger from the doors - its highly likely your window regulator relay didn't turn off either (thats what shuts it off). Fix the door pin switches so the interior lights work. Pulling the interior light fuse causes the trigger to disable the windows to go low anyway - regardless of the doors...

Test the theory by seeing if your window motors continue to work after you've opened a door...

Pull the window relay and see if current level is normal?

Alan

[drive-ability]

I like the last post at least he's matching the draw with a possible component. Its likely on a circuit that has the potential of being hot with the key out/off. I too like to fix the problem or if the component is crazy expensive find creative ways of getting things to work almost correctly. One could install a simple relay on that fuse circuit to power up when the ignition is on and power off when the ignition is off. Not perfect but do-able. When you build a jalopy like this you have to get creative from time to time.

V-8, 914, 930 gearbox

[Alan in AZ]

Avoid the band aids - figure out the problem & fix it...

Its a painstaking process sometimes - but it isnt rocket science - there are only so many places current can go and if you are methodical you can figure it out.

I threw out a likely cause based on the symptoms - easy to test...

But you can always just keep testing more around the areas of failures unti you figure it out. You do need to figure out how things are supposed to work (or get someone who knows to tell you) - but you just have to keep at it...

I'd suggest that adding more relays to a 928 is quite possibly the last thing you want to do - given the isses with the ones we have already!

Alan

[m21sniper]

Originally posted by Alan in AZ
Avoid the band aids - figure out the problem & fix it...

Its a painstaking process sometimes - but it isnt rocket science - there are only so many places current can go and if you are methodical you can figure it out.

I threw out a likely cause based on the symptoms - easy to test...

But you can always just keep testing more around the areas of failures unti you figure it out. You do need to figure out how things are supposed to work (or get someone who knows to tell you) - but you just have to keep at it...

I'd suggest that adding more relays to a 928 is quite possibly the last thing you want to do - given the isses with the ones we have already!

Alan

You could do it your way and spend 10s of hours of utter frustration,

Or you can fix every draw in the car in 20 minutes with a battery kill switch.

I utilized plan B> i am happy to report, my 928S NEVER drains the battery down- no matter how long it sits.

Cost to repair PERMANENTLY: 30 bucks.

[Alan in AZ]

It has never taken me more than 3 hours to figure out any current drain and I have done quite a few. Some done remotely by email as here (well mainly Rennlist)

I do have a battery switch already - but not for that reason.

My current draw is 14mA, it was higher when I got the car (maybe 45ma)... I want my car to work the way the factory intended - if I possibly can.

I would not spend 10's of hours but I would definitely spend a few hours on it... and a good deal of thought.

Sounds like you are happy with yours - thats what matters most.

But for me it would just be a band aid and I'd be diassapointed with the car - so wouldn't work for me (& probably most others I'd expect).

Alan