Where is the ECU ground wire located?

[MarkIII4Me]

I've finally put the interior back in and now I'm working on the wiring. Currently, nothing spliced into the ecu (WB, EVC, VPC, etc) is working. I check the power to the ECU and it is good, but the ECU grounds are not. Which wire on the main harness provides the grounds (Ground "B" per TSRM) to the ECU? It is the ground wire that connects to the block.

thanks.

 

[jetjock]

Ground Point B is on the intake manifold:

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=149

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=151

 

[MarkIII4Me]

I thought I found the B ground wire. Is it on the harness right next to the fuel injector plugs? Thing is, I grounded it to the intake mani, and now I'm not getting power to the ECU at all. Undid the ground and still no power. Strange. For the hell of it I tested the EFI 15A fuse in the engine bay. With the battery disconnected, voltmeter shows 12v when I connect the leads from the battery positive to the top of the EFI fuse. However, when I reconnect the battery to the fusebox and perform the same test, I don't get a reading. Does this mean I'm shorting out somewhere? Is there a breaker or something perhaps?

The battery is an Optima Blue top and it has never been charged since I purchased it 8 months ago. The Supra's lights still power on and aren't very dim, so there should be plenty of juice left. The voltage has been gradually dropping over the last few days. Yet it's still above 12v.

This seems like such an easy issue; I'm starting to get pissed at myself for having such a hard time with this I haven't messed with an electrical system in a very long time.

 

[kanji1jz]

Did you happen to ever figure out this issue? I believe that I have something similar going on with one of my customer's vehicles. 87 turbo.

 

[MarkIII4Me]

I haven't ran power to the car in a while. I think my problem was that I was grounding out somewhere in the engine bay since most the plugs were disconnected and I was missing most of my grounds. I now have 1/0 ga wire from alternator to battery, battery to frame and frame to block. I grounded the firewall to the bellhousing as well. There's still several grounds I see in the bay that I will need to address soon too (ie. coilpack, ABS unit, intake manifold and a ground hanging from the rear engine lift hook). Once it's all connected I should be good to go.

 

[metaphysico]

Just for the sake of it.

Also may want to make sure the immobilizer is not on. Every once in a while when I disconnect my battery the immobilizer kicks on and the car wont start, of course this make the starter not engage, but I dont know how it goes about doing it. Anyways to check for that just lock the doors with the key they unlock them that should get the alarm back on track if that is what it is.

I only mention this because it happened to me a few days ago when I pulled the batt wire to clear codes.

 

[Nick M]

I am going to repost, just so he can get a decent view of the wire color in the bundle.