I am putting together a 1987 355. I have a 1986 305 ECM. I also have the wiring harness from the 1986 305. My question is can I use the ECM (with a new PROM) and the 1986 wiring harness for the 1987 350 ignition setup. That is, the 1986 came with a HEI distributor (with the coil in the cap) and the 1987s come with a two wire hook up distributor, with an external coil; will the 1986 wiring harness work with the 1987 distrib? If it won't, can I get a wiring harness from a 1987 or a Painless wiring harness. PLEASE HELP ME!!!

The Service Number on the 1986 ECM I have reads: 16198259 (its an AC DELCO replacement model) Thought I'd put that fact in here in case it has some value.

 

The distributor is a non-issue aside of hooking up the wires to the harness correctly.

 

I did what you are trying to do. I used the ECM from a 1986 305 and internal HEI distributor and adapted it to a 1987 350 and HEI with external coil.

I went to the wrecker and cut the wires off a car that had the external coil. Most GM's after 1986 had them, 6 cyl and 8 cyl engines. Then I made an adapter to go from the large 4 prong to the smaller 4 prong connection. It cost be a few bucks at the wrecker and some time. I did not want to cut my harness.

Just make sure you match up the right pins on the plugs. I recall the small plug was backwards compared to the large one ... IE pin A on the large one was pin D on the small one. Or something like that.

Mark.