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Discussion Starter · #1 ·
So I bought a mk3 with a 1jz swap and all seemed good when I bought it with the exception of a few “minor” hiccups. There is a low idle issue that I am somewhat sure is do to the TPS and the other issue is that the car stays running for several seconds after you turn off the key. I read several threads about number 2 issue and the general consensus was that there was a wiring issue. That ended up being an understatement to say the least. Aside from the ecu being located in the engine bay (which was a red flag), the wiring harness looked to be well done. Well..... not so much. I decided to open it up and found Pandora’s box. This thing looks to be butchered beyond belief. There are 2 relays that I was told were for subwoofer wiring, turns out one is for switched power to the interior circuit and the othe is for the ecu. I feel like I got screwed so bad on this car and I bought it as something for me and my son to enjoy together. If anyone can help me get this sorted, it would be more than amazing.
So things that I know: the fuel pump runs constantly with the key in the on position. Also, as stated before, the car runs for several seconds after the key is turned off until it sputters out. The fuel pump will also run run for several seconds after the engine has been running and the key is turned off. There are so many wires cut from the ecu and so many more just hooked to power that I really just don’t know where to start.If anyone can help I would be so very appreciative.
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97 HARD TOP
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Is buying a new custom harness a option? I'm sure tweak performance could do it easily and it would save you tons of time and worry down the road
 

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Unless you're good at rewiring things yourself, it's going to be way less a headache to get a new custom harness. Otherwise if you not into spending the money pull it out and look at the wiring diagrams on here, map it all out, properly solder/shrink tube connections, change out brittle connectors and rewrap everything. Good luck working on someone's shitty wiring job is no fun.
 

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Having been down this road with several customer cars over the years - the fastest, best, and cheapest option to truly solve these issues is a complete custom harness from a professional that matches your specific model year/configuration Supra and the engine/ECU you have.

Yes, that's a $1500+ proposition, but it actually solves the problem.
 
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Take it one wire/problem at a time. It's overwhelming but it can be fixed.
Start with the fuel pump follow the wires back then remove and repair. Do the same with the other relay. The tps is an easy fix with a multimeter. Once you get that sorted it's just a matter of extending the harness.
 

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Discussion Starter · #6 ·
I worked on the harness for a while yesterday. I cleaned up all of the wires that were just twisted together (solder and shrink tube). The car is at least drivable. I think that I am just going to have to save my pennies for a while and get a new harness when the budget allows. I’m no stranger to wiring jobs. I have made several custom motorcycle harnesses over the years. However, by the time I essentially make a new harness extension to relocate the ecu inside the car, and fix all of the other crap, I feel like the time invested will just be insane. It just kills me that someone took the time to build a pretty cool car, and then wired it like an ass hat! They stood back and looked at that wiring job and said “yeah, that shit looks good!” And then taped it all up nice and pretty! Thanks to all for the responses and encouragement. I’m going to call tweaked tomorrow and try and get a bead on what kind of cost I am looking at.
 
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