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1990 GT-S W/JDM 3S-GTE Engine ECU WIRING ?

Tue Jul 06, 2021 6:57 pm

Hello Everyone.

I've been lurking here for a while and have read as many forums as I could find or have access to trying to nail down the exact wiring to sink up my Car wiring to the JDM ECU. I have found wiring Diagrams, I have the Electical Wiring Book for my car, but after wiring it up I get a click in the right kick panel "starter Relay" but no Starter turn over.

Quick background on my Celica setup. I have a US 1990 Toyota Celica GT-S Body. I took a 91 JDM 3S-GTE motor with a 95 MR2 LSD Tranny and exhaust out of a 90 GT which ran perfectly fine. In this process I noticed that the one plug going from the car wiring to the ECU only had about 5 of the 13 wires connected and it ran just fine in the GT Celica. When I swapped it over, I wired up 11 of the 13 wires and still no starty... So now I am tempted to start removing wires back to see if it will start. As soon as I figure this out I will be posting detailed pictures to help anyone else in the future, but please IF ANYONE has already done this, PLEASE send me the link so that I can see EXACTLY how they wired it up and hopefully I can figure out what I am missing.

Thank you all in advance.
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Re: 1990 GT-S W/JDM 3S-GTE Engine ECU WIRING ?

Tue Jul 06, 2021 9:37 pm

Can I assume that your 1990 Celica GT-S "body" originally had a manual transmission with a 5S-FE in it? Assuming the answer to my question is YES, as there would be no starter relay in the passenger front kick panel clicking if the 1990 Celica GT-S originally had an automatic transmission (there would be no starter relay in that junction box if the body was set up for an automatic transmission).

Also, the wiring associated with getting the starter to operate does not involve an ECU.

It may be possible your starter relay "clicks" because the solenoid is working, but the contacts may not be working too. You might want to try another starter relay or two to see if that solves the problem.

It is also possible the the relay on the starter isn't functioning also. That happens often to those starters.

I would check all this out before messing with your currently installed wiring.

Re: 1990 GT-S W/JDM 3S-GTE Engine ECU WIRING ?

Wed Jul 07, 2021 2:09 am

Echoing what 93celicaconv said, i'd check out a few things before digging into the ecu wiring.
I suggest making sure:
the starter is actually getting 12v on its big lug.
the battery is actually outputting 12v. Made that mistake myself a long time ago, never again.
the battery terminal connectors themselves are in good shape. There's a thread on this forum where someone said their gt swap couldn't spin the starter because the factory st182 battery terminals weren't beefy enough.
the starter is actually good by bridging it.
If all that checks out, next thing I'd do is look at the key barrel and make sure it's getting 12v and sending out 12v when you turn the key to crank it.

*caveat* on the st185's, there's a starter switch on the clutch pedal that has to be closed in order for the starter relay to energize. I don't think you'll be able to trace 12v from the key barrel all the way to the starter enable spade connector unless both the relay and the clutch switch are closed.

Take this if you don't have it yet: http://gt4.mwp.id.au/Toyota%20Manuals/T ... iagram.pdf

good luck! keep us updated. I think you should be able to track this down if you can trace 12v all the way thru the system and carefully bypass items to rule them out as needed. Multimeter is going to be your best friend here.

Re: 1990 GT-S W/JDM 3S-GTE Engine ECU WIRING ?

Thu Jul 08, 2021 3:32 am

Thank you both for the info, I will start testing things and try and narrow down where the disconnect is.
I have the hard book of the link you sent and have been studying the crap out of it, it might take some time, but eventually I’ll get it.

When I have a chance I’ll upload the actual wiring diagram I used to hopefully get some confirmation on if I did it right and or if I missed anything on the ECU.

Thanks again!

Re: 1990 GT-S W/JDM 3S-GTE Engine ECU WIRING ?

Thu Jul 08, 2021 10:12 am

Can we assume that your 1990 Celica GT-S "body" originally had a manual transmission with a 5S-FE in it?

Re: 1990 GT-S W/JDM 3S-GTE Engine ECU WIRING ?

Thu Jul 08, 2021 3:38 pm

Yes, when I bought it in 2004 it had manual transmission.

Re: 1990 GT-S W/JDM 3S-GTE Engine ECU WIRING ?

Thu Jul 08, 2021 5:19 pm

OK, then your 1990 GT-S has the original starter relay (and junction box) with the clutch safety switch. And you said you are hearing the click of the starter relay when you turn the switch to START, so you know that circuit through the starter relay solenoid is working.

You just need to check circuit that feeds BAT power to the starter relay is present when the switch is in the START position, and if the circuit coming out of relay to the starter solenoid has BAT power leaving it when the switch is in the START position and the clutch is depressed. Will need 2 people for that. If that all checks out, you will need to see if the BAT power is present at the starter solenoid when the switch is in the START position and clutch depressed. If it is, you need to check if you are have a good power connection between the BAT and the starter relay (the primary battery cable). If you do, tap the starter lightly with a hammer (not the relay, but the starter body) to try to get the brushes to make contact on the starter rotor. If it kicks over then, you know you have either worn starter brushes or the brushes are not sliding properly in their channels (they are spring loaded) to make proper contact. You could disassemble the starter to find out which it is. Brushes are easy to replace and also easy to clean (if debris is causing them not to slide).

I'm more thinking the problem is with the transplanted 3S-GTE starter right now than with your wiring.

Just my 2 cents worth here.

Re: 1990 GT-S W/JDM 3S-GTE Engine ECU WIRING ?

Thu Jul 08, 2021 6:13 pm

Most of the time the starter issue with the 185 comes down to a grounding issue. My car used to have the turn and click but no crank starter problem intermittently, but I fixed it with new supplemental grounds. And after I finished rebuilding just a week ago I was having the same issue again and I realized I had forgot to put the big supplemental ground I had added from the trans to the chassis. The starter gets its ground from where it mounts to the transmission. Add a big ground wire right by the transmission to left hand side mount stay ran to the chassis somewhere close (good clean metal on both) and see if it helps. Adding extra grounds helped clear up a bunch of little crap issues on my car. The OEM grounds, like the rest of the wiring get corrosion over time.


Re: 1990 GT-S W/JDM 3S-GTE Engine ECU WIRING ?

Thu Jul 08, 2021 8:03 pm

Thank you both for this input. I run my own handyman business, a wife, two daughters and a little one on the way so I only get to tinker with this here and there. As soon as I do these few things I and make some progress I will report back! Thanks again!
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