Greetings all,
As the proud owner of a '89 Volvo 740 turbo wagon with 228k miles, I'd like to be able to keep my car on the road. But I'm having trouble hunting the source of a phantom power drain, and I'm hoping there's some suggestions for where to look next.

The issue:
At rest, the 740's electrical system is pulling 0.6 amps (should be 0.1-0.2) -- enough to drain the battery if left off a few hours. I have pulled every fuse, but the drain was still there. Alternator charges the battery fine when the engine is running, and it's not the glovebox/dome light/some other bulb left on.

The only other hint I have: There's an intermittent power fault somewhere in the lighting circuit. When I turn on my headlights at first, the high beams will glow dimly; when I use the turn signal or brake, the dash bulb warning light blinks briefly. Neither is consistent.

Fixes:
I have resigned myself to looking at ground points; I haven't pulled the bulb warning relay yet, but that's about the only thing I haven't checked on the relay panel. Any tips for what to do next or what fixed similar issues would be greatly appreciated.

-- J.H.

 

bad grounds /shouldn't/ cause phantom current drains.

your high beams are on a relay that is in the main fuse/relay panel, you might pull that and see if your drain goes away, but I suspect these are unrelated problems

you might pull each relay from the main relay panel (one at a time) and see if one of the relays is in the phantom drain circuit. easier to pull the relays if you remove the cubby+cigarlighter above the ashtray, pull the bezel off the cigar lighter socket, and there's 1-2 small screws, remove them and the box comes free (exceptf or the wires to the cigar lighter, and ashtray utility light, of course).

the big red can in the relay panel is the bulb out detector, and most of the cars lighting goes through it. if you pull that and the drain stops, then thats a huge clue.

if that doesn't pin it down...

there's 2-3 wires in addition to the big fat one at the battery plus terminal. you might disconnect all those extra wires, and put your amp-meter in series with each one and the battery +, see if this pins down which wire the drain is on. one of those wires goes to the 'positive terminal', which on my 740 is under the driver side dashboard, kinda near the stereo amp to the left of the steering column, this is a flat black plastic 'box' cover with a whole pile of red wires coming out of it, and is unswitched / unfused power for nearly everything.

another of the smaller red wires at the battery + goes to the 'radio suppression relay' under the hood, this provides power to the fuel injectors. on a 91, this relay is near the right fender on a non-turbo, and the left fender on a turbo.

yet another wire off the battery goes to the electric fan relay, if you have one (91 did, I dunno 89), on 91, this relay was near the right fender.

the big red wire to the battery goes to the starter, and on to the alternator B+ ... hey, does this car charge OK? after its been parked for some hours, a fully charged battery should be around 12.6V (give or take a few 1/10ths). when you start the car and after you blip the throttle to ensure the alternator is kicked, you should see about 1 or 1.5V more across the battery, eg, 13.6-14.1V. if you don't, time to investigate the charging circuit and the main battery, alternator, engine ground straps

I don't have older 740 wiring diagrams handy, just 91 & 92 (mine is a 1992), but AFAIK, most stuff is pretty close to the same thing on a 89 (which was also LH2.4 injection).

 

This is all good to hear; I started the pull test of the relays today, but didn't make it through all of them (the red "coke can" relay is a real PITA.) The alternator has been charging fully after I replaced the ground wire; I get good readings on the dash voltmeter and 13.5-14v across the battery terminals.

I'm also glad you listed the positive battery cable; that's on the replacement list anyway.

This is a problem that a nearby expert Volvo mechanic turned away, which has only made me more determined to fix it. I'll keep the thread up to date with any progress.

 

89 /should/ be after the window of biodegradable wiring, that supposedly ended in 87.

be careful with that red can, thats the bulb failure detector and its fairly fragile inside. its a mess of reed relays and coils inside... the main beams (not high beams), brake and parking lights all go through it, so with it unplugged, those would all be disabled.

it detects a bulb out by having both lights in a pair go through counter-wound coils on the same reed relay. if the current is the same in both coils, they cancel each other. if one is on and the other off, the reed activates, and lights the bulb out sensor.

I've never unplugged mine, so I dunno if there's a trick.

an 89 turbo 740, thats probably LH2.2, even tho the 89 non-turbos were LH 2.4 ? there might not be a radio suppression relay on a LH2.2 car, I dunno quite when they were added... as I said, I don't have any greenbooks covering the 740's prior to 1991 (I have the 91 and 92 because they are the same as 940's of the same year, and I have a DVD with all the 9xx series greenbooks).

 

Pierce is right about the difference of the 89 year. I happen to have and 89 740 Turbo wagon too. I also happen to have a full wiring diagram for the car (from the new car features for 89). They came out with a revision for that year. I stitched it together in Photoshop the other night and here's a link to it: https://skydrive.live.com/redir?resi...F7Bsa7QrnqUjGw. It's quite long and you can divide it up and print it off if you like, or look at it on a computer. The key is at the far right. Maybe this will help you troubleshoot. You should see everything that is connected by a fuse and what is not. That should cut down your search. Also, this diagram covers every car for every market (the "turbo +" wiring is even on this) so you'll see a few different fuel and ignition systems as well as euro head lights, American head lights and other accessories. Enjoy!

 

ah, and heres the greenbook version,

VOLVO 740 1989 - wiring diagrams

much easier to read, and each section has a locator drawing

its too bad there's no index to the pages, you just have to scroll through it


edit: ooops, thats just the engine stuff, not the whole car.