It's me on the sierra forum, Ford Power, Powerd by ford, XROC, MK1 golf, Galaxy owners... I am all over the place, and a few computer forums too
91 Should be a single fusebox car, the ECU loom should unplug from the car loom with two multiplugs ( if I remember rightly ) . with that undone you have the standalone engine loom. If the plugs are the same as the 24V V6 then you will find the details of the pinouts of the plugs on my website.
TT