This is the original Supra wiring instruction printout that someone made over a decade ago. I forget who made this guide. If you know who it is, please reach out. These are not exact instructions, but the color coding does help. This basically tells you how to wire the US 7m harness ends to the jza70 harness. The idea was to create a plug and play harness for your US Supra.
At the bottom of this page, you will find a downloadable PDF version of this.
At some point I will edit these pictures into step-by-step instructions. You should read about HARNESS EXTENSION as well.
B1 to IH1 Connection – B1 is the big fat connector near the ECU. On the early MK3 there are 22 pins as shown below.
M1 to IG1 Connection – The M1 connector carries most of the gauge cluster signals. Since the JZA70 is much different, you must convert it.
EA2 to C1 Connection. This is the plug near the battery area. The c1 connector carries relay power. Also, the JZA70 EA2 has the alternator wires, so you would wire this to the alt plug. The alternator is on the other side now, so you should extend the wiring accordingly.
PRINTABLE PDF – Here is the full PDF of all the pages from this writeup.