ok so i got some pictures to show you what i mean about how you can use any ecm from 1990-1996 on your truck.
If you have different connectors than the ones shown going into your ecm than its a 1994-1996 cal emission harness. these are rar to find so you dont need to worry.
so if you have a 1993-1996 harness like the one shown and you want to use a 1991-1992 ecm just move that wire over. this is on the center plug going into the ecm btw.
also here is an image of a 1991-1992 harness, its not real clear but if you look close enough you will see what i mean
I have personally tested both styles of ecms on both 6bolt and 7bolt motors and they work fine on both.
So now the secret is out that you dont have to spend $115+ on a 1991-1992 when you can get the 1993+ ecms for 45 bucks on ebay.
A Side note: the 1991-1992 ecm in my opinion has a slightly better idle than the 1993+ ecms and that goes with when its paired with either 6 or 7 bolt motors. the 1993+ works great though. either ecm is good for smog in cal. ive use both combos sense ive had my trucks.
this info goes out to those poor folks with a 1990 mighty max like myself.
the 1990 mighty max has the same wiring going to the 1g style MAF as the 2g style mighty max MAF. You can simply cut the pigtail off a 1991-1996 mighty max maf and splice it into your harness. the wire coating is even the same between the two. the one thing that the 1990 mighty max does not have is the MAF Reset wire. You will need to grab this wire when converting your 1990 to use a 1991-1996 style MAF and ecm. YOU CANNOT USE THE 1990 ECM WITH THE 1991-1996 MAF. so if you do this be safe and create a duel connector like this.
this way you can swap between MAFS and ECMS latter if you want.
Another side note for 1990 guys. this year came with different injectors than the 1991-1996 mighty max trucks. they are the same flow and cc but have a different part number and are specific to this year. This may sound far fetched but i have also tried the 1991-1996 ecms with them and they work fine. i did notice a tad bit more fuel consumption like going from 23mpg to 22mpg. nothing big and i did do smog like this.
I Hop[e this helps you and answers all your questions. I Love this site and love these trucks.
Final notes. i posted this in another thread both thought that it deserves its own thread so if someone searches online they will see it. I have gone threw the troubles of the ecms on these trucks and it sucks.