Wiring is one of the biggest hurdles to get over in this swap. A basic understanding of automotive electronics is needed. My goal is a little different than most when it comes to the wiring. The standard approach is to mesh the two harnesses (the MR2’s to the 20v’s) by soldering wires together or rearranging pin outs into custom connectors. I was not interested in cutting up my MR2 harness. If I ever need to put a 16v back in the MR2 I want to be able to do so with out much hassle. So my approach has been to create an adapter harness to connect the MR2 harness to the 20v harness. In order to do this I had to use connectors off of my parts car. These can also be sourced from your local junk yard. I have found a few differences in some of the systems that require me to tap into wires at the MR2 fuse box but no cutting as of yet.
NOTE: This write up is not complete as I am not done with the wiring yet. I might determine later that some of the information is not correct. So just take it as it is. Also this wiring is for an ’86 MR2 5-speed and ’97 Levin BZ-G and might be different than what you have. Try and use this as a guide as to how the systems work not to find out exactly what wire goes where.
On the MR2 side of things there are 3 main connectors that are going to be used to mesh with the 20v engine harness.
The Molex-type connector is found in the middle of the trunk. This connector connects the MR2 body harness (with the fuse box) to the engine harness. The Grey connectors can be found underneath the fuse box close to the battery tray. On the 20v side you will be working mainly with the connectors that connect the 20v engine harness to the body harness.
This is the schematic of my adapter harness to go between the MR2 body harness and the 20v engine harness. I don’t think it’s 100% complete, there might have been some changes for the alternator that I had to incorporate while working to get engine running, but it’s as great starting place: