88 7mgte auto major electrical prob

[Noel]

A friend of mine just got an 88 7MGTE. Problem is the previous owner tried to boost the car with the boost cables set upin reverse polarity. the end result was all the resetable breakers (2 on the junction block on the driver side and one on the passenger side needed to be reset. Now the situation is the 7.5 Amp Ign fuse on JB-1 continues to blow. We have disconnectged the ECU and the alternator and pulled all the fuses except AM1 and the Ign fuse, which is supposwed to feed the ECU still blows when the ignition is turned on. We have also tried disconnecting the fuel relay, thestqarter relay and the O2 sensor as recomended by a Toyota Mechanic with years of experience.
In the few seconds before the Ign fuse blows the windows work. Once blown only the door chime works. I have been able to find most of the wiring diagrams and as far as I can see only the charge light and the feed for the ECU are loaded on that fuse.

Any one with some ideas would really be appreciated.

[MA70-3.0GT]

I wonder how long he had it connected in reverse... long enough & it's possible he could have melted insulation somewhere in the loom causing the problem you now have :/ There's some good wiring diagrams & troubleshooting info here http://www.cygnusx1.net/Supra/Library/TEWD/MK3/

If I get time I'll have a look see later, see what's on that circuit that could cause issues but the fact that the windows work without their fuse & stop when the IGN blows would suggest melted loom to me at the moment...

EDIT-: as the windows stop when the fuse blows, are you sure it is definitely the IGN fuse and not the 7.5A GAUGE that's blowing? I say this because this fuse operates the power window relay amongst other things. If it is GAUGE then the loom may be OK after all & you need to check the circuits related to that fuse instead ( Can't copy/paste them but theyre listed here http://www.cygnusx1.net/Supra/Librar...x?S=Main&P=032 ) Also, as it takes time to blow the fuse I'm led to wonder if it's related to either the ABS or ECT systems, possibly something in their self-test regime that causes the fuse to blow after XX seconds?