'87 Caprice 305 wiring from the computer unit

[deesandvees]

I've got an '87 that came with the 305 and I'm going through every single wire that comes out of the firewall. I've got the factory service manual and factory electrical supplement also. The left side was easy, headlights, windshield wipers, etc., because the electrical service manual has a diagram of that harness connection at the firewall with all the wire colors and everything. But I'm on to the right side and can't seem to find what I need to figure out the big bunch of wires coming out of the firewall on the right side under the ac box. I want to make sure I know what all this is because I'm getting ready to hook up my rebuild (383) with an edelbrock performer carb and I know it seemed like there was a million things hooked up to that electric carb that's now sitting up on a shelf in my garage collecting dust.

[silicon212]

I hope you're not expecting the computer to work!

The large bundle of wires that 'comes out from below the A/C" is the computer harness.

[Blue Bowtie]

A 383 is about perfect for a QuadraJet. Why limit yourself with an Edlebrock clone of a Q-Jet? The E4ME can flow up to 780 without modification, more if you tinker. Beyond that, you'll be able to keep the ECM and program timing curves that are impossible with any mechanical/vacuum distributor.

I'd keep the carb and ECM wiring intact. You can find schematics all over the www, like at autozone.com

[deesandvees]

I might be keeping the q-jet at this point. I need to go through the ECM harness though and can't find schematics on that mess of cables coming out of there. There's a couple wires that I see are severed with no ends on them and a couple very small vacuum tubes that go to nowhere. Any help on that?

[silicon212]

You can get the Haynes 1969-1990 Chevrolet B-body manual, which has schematics at the back of the book. It doesn't specify wire color, so you will need to trace the wires to their sensors.

The two vacuum lines should be the A/C control. The brown one will go to the heater bypass valve, and the white one will go to the vacuum supply, which is usually an orb-shaped reservoir on the A/C evap housing.

[deesandvees]

Thanks Silicon, I've got the factory service manual and the electrical supplement too, does it have this info in there? I was able to identify all the under hood wiring coming from the fuse box with the electrical manual but not sure if there's a good resource for the ECM in there, at least I couldn't find a page as easy to understand as the page for the fuse box harness. If not I'll get the Haynes.

[randy78]

the books arent going to tell you everything about every ECM wire

there were many different variants of the ESC and EST carb systems

some had knock sensors and some didnt, some had AIR pumps and tubes and some didnt(wires for the pump and parts are inside the same harness), some had a different number of wires running to the carb than others, such as some of the 80s 305 trucks that only had a single black wire running to the top of the E4ME carbs, unlike most other E4ME carbs

and some had sensors that others didnt,

all depending on the exact make model year and selling/dealer location it was built for

48 state

federal

canada and so on

you wont get every wire detail in any given book schematic


what exactly do you need to know

what are you trying to do ?

you have to make up your mind if you are going to run ESC/EST or not

if no then remove that entire harness

if yes then leave it alone


pick one

good luck!

[deesandvees]

That's what I ended up going with, ditching the entire harness. Thanks for the info.