Electrical Gremlins - Toyota Nation Forum : Toyota Car and Truck Forums

Micchi · 08-28-2007, 09:38 PM

I've been a lurker here for a while, but I figure this one's enough to make me come out of the woodwork.

I've got a pretty little blue '83 Supra. Sure, there's some body work that needs to be done -- the fenders are dented in, there's rust there and on the hatch, and I have a suspicion that the Russian Mafia is responsible for my lack of radio -- but he runs well. I've put a good deal of work into the car, but most of it has been routine maintainence (replacing belts, getting a battery and an ignitor, replacing the radiator when it went kaboomsky). Now, though, I've got a big problem I've been trying to work out to no avail. I'm going to have to send it to a mechanic; for starters, it's on the other side of the country from me. (Augh!) But I figure it's worth a post to see if I can narrow down the problem and not blow a fortune on the poor boy.

The fuse for the interior lights and tail lights keeps blowing, and I have no idea why. I've poked at it, the family mechanics have poked at it, and no one can figure out what the problem is. What happens is this: I put a fuse in. The fuse is new, it's shiny, it's the right fuse for the job. I get in the car, start it up. Flick on the headlights. The lights come up, the interior lights turn on...and then they click right off. Oh, the headlights stay on, but the tail lights are gone, the lights for the instrument cluster the same. There's no crack, no pop, no earth-shattering kaboom. Just on, then off, like a light switch. Everything else still works. The only other fuse that blows on a regular basis is the clock/horn fuse, but that's still nothing like this.

I'm afraid of the solution to my problem being "Honey, you need to just re-wire everything", but that's shaping up to be it. Anyone with ideas on how to avoid this utter nightmare will be placed in the Big Book Of Heroes.

CRE · 08-29-2007, 12:47 AM

There are a couple possibilities. You have a short, not doubt about that... it just a question of where.

With a MKIII the first suspect would be the tail lamp failure module. If the MKII has one it's going to be in the trunk/hatch area (on the MKIII it's a small yellow box, with wires plugged into it and it's mounted right beneath the driver's side tail light). Then I'd inspect the tailight housings for shorts, broken wire insulation or water.

The next thing you can do is buy a multimeter and start following the wiring and testing the positive wire for breaks and shorts to ground.

Jeeves · 08-29-2007, 02:51 PM

CRE, he said it's an 83., That predates the MK3. I don't think the Mk2's had LFM's.

CRE · 08-29-2007, 03:28 PM

I saw what model he/she said it was and properly qualified my statements. I don't know if they have one or not...

[quote=CRE]If the MKII has one it's going to be in the trunk/hatch area (on the MKIII it's a small yellow box, with wires plugged into it and it's mounted right beneath the driver's side tail light)./quote]

Micchi · 08-30-2007, 10:18 AM

She.

I've gone over the tail lights extensively...that was my first instinct, make sure that the wires leading to those lights were in good condition. Everything checked out alright, in one piece. It was the first time I've ever been sad to see something in good condition on that car. (At least if that had been the problem, I could have fixed it.)

I'll pass on the multimeter suggestion to my dad, who's in custody of Meg right now until I can get him back across the country.

CRE · 08-30-2007, 10:40 PM

I suspected that was the case.

You could also start checking the wiring junctions, all the plastic clips where the various segments of the harness meet. It's also possible that the short is inside the light switch. Again, IF the MKII wiring is like the MKIII (and most other Toyotas, for that matter) the switch's contact is grounded when the headlights and markers are turned off. This is to prevent the taillamp relay from latching due to errant current in the system.

Not long before this all began was any work done on the car? new stereo, other wiring fixed and so on

Micchi · 09-02-2007, 04:43 AM

Oooh. Good idea on checking the switch. I'll relay that one.

The poor boy had been taken almost apart before I got my hands on him. The horn/clock fuse was blowing more often than I was comfortable with (once every two or three months), and I was going to take him in anyway. I had a stereo put in as he didn't COME with one (but hey, for $300, I ain't complaining), and that's when the trouble started.

If I had ANY clue what I was doing electrically, I'd have put the stereo in myself. I've got a family friend and mechanic taking a look at him now, though. Hopefully, HOPEFULLY he can figure out what it is.