Positive terminal wires - chasing mystery short
 

Hi all,
I have a 1994 940 4cyl, non-turbo, gas. solid car. Something has started to draw amperage off my battery when the car is turned off. I measure 120 milliamps. I pulled all the fuses, and the clock/radio/interior lights (fuse 5) dropped it down to 90 milliamps. No other reduction in amperage was seen from pulling fuses.
I pulled apart the three wires on the positive terminal and tested those. One, a black wire with a boxy connector had all 90milliamps drawing through it.
I reconnected the wires but left that one off and nothing in the car works, no lights, won't turn over etc.

Where does that wire go?!?

Thank you for your help, i'm going to track this thing down!

afaik, all factory wires at the battery + terminal are red. the big heavy wire goes to the starter and alternator, one wire goes to the 'positive terminal' which is a small junction box of red always-on wires located near the brake pedal under the drivers side dashboard where most everything else is connected. Another wire might go to the 'radio suppression relay' under the hood which powers parts of the fuel injection system.

is it possible this car has an aftermarket stereo amplifier or any such accessories added to it? power for a trailer brake light controller?

I've attached a picture that might help clarify.
http://nathanhodges.net/IMG_2439.JPG

there are actually five wires on closer inspection that come from the positive terminal.
One big red one that i assume goes to the alternator/starter
and a bundle of three smaller red ones.
then a grey one.
short is in the bundle of smaller red ones

the BIG one on the clamp goes to the starter, and there's a wire from the starter to the alternator.

the 2-3 red ones look like the factory wiring, those other two almost look added. kind of looks like its been redone by people?

ok (digs up the 1994 greenbook tp-3904202)...

yeah, lets see.. there's 3 red wires... The first 2 wires go to the positive terminal, which is is a small flat black plastic box with a bunch of red wires behind the dashboard that is screwed to the firewall, near the (missing) clutch pedal pivot. The 3rd wire goes to the radio suppression relay, which powers the fuel injection.

there's a 4th red wire to the ABS.

on a diesel, there's a wire to the glow plug relay (might be the same wire for the FI)


everything, I mean EVERYthing else comes off 15/1, the 'positive terminal' behind the dash.

oh. missed one. fused 'GREY' wire from the battery + to the engine fan relay.

great!
So the "positive terminal" under the dash... what systems does it power? once all the systems that go through the fuse box are eliminated as potential causes of the short, what's left that comes through the positive terminal?

*EVERYTHING* that I didn't list above is connected to the positive terminal.

the ignition key has two red wires off it.

the always-hot bus in the fuse/relay panel has 2 more red wires.

pretty much everything else in the car that needs power is connected to it.

I'd try unplugging the radio suppression relay, on the left fender behind the power steering stuff.... see if thats your drain.

pierce you're awesome!

disconnected interference suppression relay, no change.

a couple of questions.

the overhead light in the car when in the position where it turns on when the doors open, off when they're closed, never turns off. it's on whether doors are open or closed. Each door switch is good as evidenced by the fact that the small red lights on each individual door are turned off and on by the switch.
is there another circuit or relay that keeps that light on for a few moments after the doors is shut?
pulling fuse 5 that powers the courtesy lights turns the light off

and question two, this one is silly,
on my digital multimeter, i'm using the 10amp setting. the readout say "0.09" i assume that's 90 milliamps, but not totally sure.

thank you all!
nathan

on my 1992 740 and I think all the 940s, the dome light is on a timer when you open teh DRIVERS door, but the other doors don't invoke the timer. the timer circuit is in the dome light assembly. I'll have to look at the wiring diagram again, but I think there's two switches in the door button..... yup, there is. the button grounds both wires when the door is open, one wire goes to the in-door light at that door, the other switches are ganged together and go to the dome light pin 3 (black) such that if any button is unpushed, the lights come on. the driver door courtesy light side also goes to the dome assembly pin 2, which triggers the timer.

on a 10 amp setting, yes, 0.09 amps would be 90 milliamps.

you said you've tried pulling each fuse, and still see this 90mA drain on that red wire... try pulling each relay on the main fuse panel, one at a time, and check to see if one of them stops the drain.

How many amps does a 1994 940 usually pull when the car is turned off?

mostly, its the clock and the radio standby. I'd guess it is like 20-50mA, but I haven't measured.

What I don't understand is, if the short is not in the fused systems, and not in a critical system (the car runs fine, just took it on a two hundred mile road trip, no problems). Then where could the short be? What's left?

well, what you have isn't a dead short, its a current leakage, something isn't turning off. a dead short would be melting down wires or blowing fuses.

Pulled all the relays, still have the 90mA draw. disconnected alternator in there was a bad diode. still have 90mA. Alternator is charging at ~14V.
ignition switch?

ok, I just measured 70mA on my car (1992 740 turbo wagon, with an aftermarket stereo but no amplifiers or anything), so 90mA is perfectly within reason. thats less than 0.1 amps, it would take 1000 hours to flatten a car battery with that.

so on the advice of a mechanic I went ahead and put in a new battery today. hopefully that will fix everything and the 120mA draw with key off is just 'normal' for the car.

120 ma sounds high.

I just realized my 70ma measurement, my tailgate was open, and I've got a LED interior light... 70mA, probably 50ma of that might have been my light. whoa, LED vendor's page says the red 6 cell LED I used is 85mA ?!? hmmmm.

so I'll need to do that test again, hah.

I had a issue with starting my 1990 Volvo 740 and found the electric cooling fan was was drawing power causing the the vehicle to stall and then died. I replaced the A/C relay under the right engine area. Did found a red power wire attached to the battery positive post. I am looking at the Factory book but not seeing how the wire sends power to the fan? Positive switch?

You are on a 8 year old post, better start a new one.

Tire change and now no power
 

So I just changed the two front tires on my 98 s70 base and when I lowered it, somehow all power to the car is now cut off. I had it running when it was jacked up but something happened when I lowered it. I am lost as to what could be happening. All fuses are good and the battery is brand new