HELP: Intermittent fuse/ wiring Issue- 88 MA70

green jester

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#1
Model type: 1988 JDM MA70

The car is blowing fuses on an intermittent basis whereby I cannot say exactly what causes the issue.

The issue started after I had put the engine back in after removing the engine and box for basic maintenance and an inspection for oil leaks.
No electrical components were added/ changed (however the loom was obviously unplugged and moved).
I did re-solder the knock sensors and change over the plugs on the gearbox reverse sensor plug and the coolant sensor plug on the thermostat.

Initially the car was fine, I drove it around a few days before anything happened.

Then one night I was driving home, turned a corner, straightened and the fuse blew- the engine stopped, I lost the lights and dash lights. I managed to roll into a side street and park. Tried to start the car and the starter going but not catching- no ignition: no ECU.

I discovered a fuse had blown;
The fuse being blown is the 'unmarked' fuse in between the 'Gauge' and 'Stop' fuse.

View attachment 59245

When I first blew the fuse I am sure I pulled out a 10 amp fuse, but have since consulted a friend (with a JZA70 though) who says he has a 30 amp in his. (Can people please confirm?)

I replaced the fuse with a 10 amp fuse and the car was fine. I drove around (locally, short distance) for a bit during the day (no headlights) and then the fuse blew again. I rolled onto the side of the road, threw another 10 amp fuse in again and off I went.

When I got home, I went over the engine to look for loose grounds or anything obvious that might contribute. I found one of the plugs to the horn was unplugged. So I was hoping (on a whim) that was it- it wasn't.
I went for a drive locally and blew another fuse, I then ran out of 10's and put a 15 amp fuse in. It also blew the 15.

I then drove around 80 kms (49.7 miles) to a place where I was to get some head work done. The car blew one fuse early on (3 kms in), then didn't blow one for the remainder of the journey.
The car then sat for two months (outside exposed the weather).

I then got the car back with the new head and other bits and pieces. Nothing electronically was changed aside from a bigger starter motor.

The car was fine for around a week. I drove it in the day and night (headlights/ no headlights) and everything was fine. It then blew again during the day after turning a corner and straightening.


I then looked into it closely and found that everything on line/ circuit 'E' (see link below) dies when the fuse blows; Hazard lights, headlights, horn, dome- auto antenna.

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=D&P=3

So something is happening on that circuit.

I have tried to simulate the behavior that causes the fuse to blow but have received inconsistent results:
The car was parked and running- headlights on, hazards on, break lights on- fine.... turn the radio on (auto antenna)- the fuse blows.

However when the fuse would blow when I was driving- I did not touch the radio and headlights were on in some instances and not in others.

Everything seemed to suggest the fuse size was incorrect as it was not handling the load from the combined components (headlight motors, radio- antenna motor, turn signals).

So I put a 30 amp fuse in and went for another short drive. It was during the night (headlights) and I drove normally. The car seemed fine for about 8 kms but then the same issue happened again- the engine dies, I lost headlights and dash lights, etc.

I then went to change the fuse but discovered that the 30 amp (replaced instead of original 10) had not blown. So I checked every other fuse and found that the 20 amp 'DOME' fuse in the engine bay had blown. Replaced that and it was fine. The 'DOME' fuse is also part of the 'E' line/ circuit.

The only thing that seems to be consistent with each occurrence is when I turn a corner and then straighten. I thought maybe it was the canceling of the indicator but I can think of one instance when the fuse blew and I was not using the indicator- going straight through a big round about.

I am thinking that maybe water has gotten into the antenna motor and causing a short...?

So- has any one had similar problems and/ or can advise what may be causing the issue and ideas of where to look, etc?

Thanks for any help (and for bothering to read this far).

LG
 

green jester

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#2
Any experience with this issue, area to look at? I'm fairly sure- the fuse is blowing when the indicators cancel.
 

Satan

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#3
Bump from way back... I am having a similar issue. Anyone else? Any resolutions?
 

3p141592654

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#4
In my experience for almost all cases where fuses blow on bumps, turns, acceleration etc the cause is wiring that has come loose from its tie straps and has rubbed through the insulation and is intermittently hitting the body or engine.

The most common case is the harness running through the intake manifold. The straps breaks and it sags onto the runners or EGR pipe and then rubs through the insulation. When the engine twists on its mounts the wire contacts and the EFI fuse blows.

So what fuse blows on your car, and under what conditions?
 

Satan

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#5
That was the issue (hopefully). Just enough of a short to have continuity between ground & power, but not enough to blow the fuses. I traced it to the headlight circuit, then the symptom travelled to the dome, horn-haz, and other fuse at the fusebox. I traced the whole front body harness, then removed the dash to get to the rest of the wiring. Found that the aftermarket alarm maybe had a wire that was frayed (somehow touching the return spring on the brake pedal). When I installed the alarm years ago, I removed the dash to hide the brain/modules, so it was kinda the only way to get t it. I fixed that wire and so far, so good. No continuity between power * ground. I am attaching the cluster tomorrow and gonna drive it aroun w/o dash for a bit, just to be extra sure (before putting dash back in).