ok , let me clear the harness stuff.
Its a 89 Mirage turbo shell, it has the front harnes for the alt,lights and all that, it doesnt have the ECU (engine) harness that goes form ECU to the fuse box underneath the hood. I have been told a harness form 91 eclipse,dsm... will plug in, evrything will work, as long as I keep evrything from 91 such as, tb+sensors,coil pack,transistors,ecu,cas.
Your sayin a 91 "ecu"/ "engine" harnes form a 91 4g63 won't plug into the mirage ?
IF you keep your engine, ecu and engine harness all '91, then you are almost there. That is what I'm running right now.
You WILL need the tach filter to get a working tach. The C/S/M cluster does not understand the signal from the '91+ coil pack. I suggest hooking it up to the engine with it out of the car if possible. It just makes it that much easier to get those stupid 4 bolts out. (But it is not too nasty if it is in the car, that is how I did mine)
Now, I am not sure but I think I have a GVR4 engine harness, so YMMV. Assuming it is the same thing it will NOT plug into the chassis harness AT ALL. You will need to do plenty of work to get it all happy. 95% of the wires mate up color for color though so it just is a PITA. You will need to run a line from the relay box thing (MPI relay?) to a plug up under the hood fusebox. This is right out of the howto here on the forum.
I did all of my wires with those little blue vampire taps first, then after I finally got everything working I spent a day with the solder + heat shrink to clean it all up.
One more important thing. The harness I have does not fit quite right(again, YMMV). All the wire lengths are a little bit long or short. Nothing too bad (all in the HOWTO). The one thing that I dont remember if it is in the howto or not is that the lenght of wire on the ECU harness between the firewall rubber-duckie and the ECU plugs is not long enough to reach the stock C/S/M location very easily. Since I pulled out my A/C, I just used that hole to route my ECU harness through. That took up some of the extra slack in the engine bay while giving me a little more play under the dash. It is still pulled pretty dang tight but at least it does reach.
In hindsight, I should have just relocated the ECU. Although I'm not really sure where I would have put it.