A 1986 Cab Now has Throttle Body Injection TBI

[57ToyBox]

I'am in the process of converting a 86 cab to adapt to my 87 4x4.

I've managed to upgrade the fuse box to accommodate the two addition fuses for the ECM1 and ECM B
But I'm having a hard time finding a wiring diagram to wire the ECM under the dash. My help cut the five wires from the old cab and don't remember were they go.
Any help would be greatly appreciated

[Greenlee]

I used an 83' cab on an 87' 4x4 with the wire harness from an 89' Suburban. I have wiring diagrams. However, I don't know what wires you are asking about. If you post the colors and location I can try to look them up. I really didn't have to cut any wires. The harness just plugged in.

[57ToyBox]

It is difficult to describe and all the pictures I take seem to NOT help either.
All I can say is there are two wiring harnesses on the ECM.
One that enters the cab through the fire wall that goes into the ECM and the
second wiring harness runs under the dash to the driver's side of the cab.

The only wire of this second harness was the pink/black that connected to the back side of the 10amp ECM fuse.(that was the obvious one) the remaining brown wire, black wire and one two conductor plug and a three conductor plug I'm not sure of there proper home.

[hatzie]

If you still have the 87 cab why not pull the whole TBI cab harness? It's not that complex and there are only minor differences from the 86 - 87 cabs. 99.9% of it is under the dash.

Since you've already begun to chop up the 87 cab harness you're committed now.

I posted all the 73-91 GM CK RV wiring diagrams in PDF format. Download the 86-91 wiring diagrams.
The 1987 GM diagrams are not easy to follow.
The 89 diagrams are fairly easy to follow without too many changes from 87. The 1990 & 91 wiring diagrams have harness routing info.

[57ToyBox]

Agreed Hatzie "There is only a few minor differences in the 86 and 87 cab harnesses. So I did pull the the harness out of that cab before I scrapped it.

But putting it in the 86 cab seemed pointless when all I needed to do was do the changes to the 86 harness to bring it up the the 87 standard. Which only involved providing power to the two ECM fuse locations.

I'm beginning to wonder if the gauge cluster requires any of these additional wires to up to it.
The research continues... I'll llet you guys know what I find out.

[silverbear]

This is what I pulled from my 87 cab. One wire was cut and the other terminal broke off so not much help identifying where those two go. Hope this helps at least a little.

Chris

[57ToyBox]

Yeah.. That's very similar to my harness. But those plugs and connection are from the engine compartment side of the fire wall.
I've got that done... I need to figure out the UNDER DASH connections from the ECM to the fuse panel and gauge cluster.

[silverbear]

Oh sorry. I am going the opposite route and removing the ECM because I am running a carb. I will double check my left over wiring harness this afternoon for the cab side of the wiring.

[57ToyBox]

That would be greatly appreciated.. I'm thinking if this doesn't work out... I'm gonna do away with the throttle body and go back to the carb.

[silverbear]

Sorry Glenn, it appears that I don't have the same set up. I checked all my loose wires and stray connectors and none of them match your description above.

[hatzie]

A picture would help a bit...

[57ToyBox]

Here is a picture of the ECM. The small wiring harness (wrapped in tape) heading towards the driver's side is the one I DON'T know were it hooks up to.



Here is the end of the small harness.

[hatzie]

Download three of the wiring diagrams 1986, 87, & 88 from my manuals post in my signature. Open the 1987 & 1988 diagrams. 1987 PDF page 175. 1988 is spread from PDF pages 284-290 but is easier to follow.

The plug below the brake pedal probably goes to the neutral safety switch.

• Orange/Black ECM PARK/NEUTRAL SWITCH
• Black/White SYSTEM RETURN (ECM Ground layer)

The plug in the lower left looks kinda like the ALDL (Assembly Line Diagnostic Link) plug. The two wires with dangling female Packard connectors should both go to the bulkhead socket.

• Tan/Black is probably Circuit 422 in the bulkhead socket. 422 goes to the Torque converter clutch, ECM and kickdown relay via the engine compartment.
• The other hanging female Packard connector wire runs to the center of the ALDL plug next to the White/Black wire? If so... it's circuit 436 in the bulkhead socket. 436 goes to the IAC and ECM via the engine compartment.

The 1986 wiring diagram shows these bulkhead socket positions to be unused...

The Pink/Black wire is probably one of the Circuit 39 or 439 Switched Ignition Power wires in the harness. Fuse panel IGN power sockets?

[57ToyBox]

Thank Hatzie
You have definitely have give me some home work. I REALLY appreciate this.
I will have my work cut for me tomorrow Sunday. I will be sure to let you know how I did.
Thanks again

[57ToyBox]

Originally Posted by 57ToyBox

I made some progress today
The plastic white plug has now found it's home again on the Speed Sensor
The black plug goes on the Neutral Safety Switch on the steering column.
The remaining two wires will go somewhere on the fuse panel

Tomorrow I will be picking up a Backup/Neutral Safety Switch
Thanks again Hatzie for your help. Updates to follow

[57ToyBox]

I have got a new backup / neutral safety switch both the pair terminals have a wire but the loan terminal doesn't. Does anybody know if this loan terminal have a wire assigned to it?

[57ToyBox]

I have got a new backup / neutral safety switch both the pair terminals have a wire but the loan terminal doesn't. Does anybody know if this loan terminal have a wire assigned to it?

[57ToyBox]

The two side by side terminals are the back up terminals and the two brass terminals over each others are the ECM terminals. The terminal all by it's self I'm unsure about. I don't know what it's meant for.

[hatzie]

Originally Posted by 57ToyBox

I made some progress today
The plastic white plug has now found it's home again on the Speed Sensor
The black plug goes on the Neutral Safety Switch on the steering column.
The remaining two wires will go somewhere on the fuse panel

Tomorrow I will be picking up a Backup/Neutral Safety Switch
Thanks again Hatzie for your help. Updates to follow

So is that plug in the lower left the ALDL?

[57ToyBox]

Yeah it was the ALDL
It's now mounted under the dash beside the Ebrake release

Now I need to find a home for the two wires with the green tape on them
And there is a fifth post on my new Neutral Switch I don't have a wire more

[hatzie]

Reading the 1987 wiring diagram sheets is nasty till you figure out what GM did and why. It's still nasty to read but you can kind of navigate it...
The perimeter of each page has numbers and letters to locate XY positions on the drawing as if it's printed on graph paper. Horizontal "X" numbers and Vertical "Y" letters. Each wire has a grid position column to tell you where to find the other end of the wire.
Next to each component or connector the wires have alphanumeric characters in 4 columns.
GM Circuit number, "XY" Grid position, Wire diameter in mm², and wire color.

The 1987 wiring diagrams PDF page 177 shows the termination positions for the ALDL circuits...
The ALDL plug is at diagram Grid position K19.
According to the diagram the loose wires go into the bulk-head socket at diagram Grid position W7.
The Tan/Black wire is from ALDL socket position F (TCC) Circuit #422 and unless I'm mistaken the other wire is from ALDL socket position C (AIR) Circuit #436.
The solid black wire from ALDL plug position A (Ground) is Circuit #450A and it goes to a splice with 4 other black wires in the harness at diagram grid position U24 so I doubt this is the loose dark wire...

As long as ALDL positions A (Ground), B(Diag) , & E (Data) are populated and properly terminated this is all you'll ever use. Data Pin E is useless without a Tech I or maybe an ALDL enabled diag tool like Craig Moates WinALDL.

The lone terminal on the neutral safety switch is probably for other models that switch can fit. The 73-91 trucks don't have any other wiring there AFAIK.

[57ToyBox]

Just to update... I still haven't had any luck breathing life into my ECM or my fuel injection.
BUT I do have some good news. I just came upon a deal a couldn't refuse. I'm going to pull a 1990 Chev Blazer 5.7L w/ tranni This time I will clearly mark every wire and it's detailed location as it come out of the truck. I'm actually excited to be rid of the 305 and into a 350 with a serpentine system

[hatzie]

If you're going to the 1990 setup... the 1990 bulkhead plug has some very significant connector position differences from the 1986 & 1987 bulkhead plug. You will not just plug the 1990 engine harness into the 1986 cab and go...

I would highly recommend pulling the whole cab harness along with the engine bay harness. It'll be easier to make it go. Get the forward lighting harness as well. There's really not much to it... You won't be kicking yourself later for not taking it either.

I take pictures and use blue or green painters tape. I record stuff in a cheap spiral bound notebook with copious notes...

[57ToyBox]

Back to square one.
I walked away from the 1990 350.
Turned out the engine hasn't run in a few years, Pullys were very rusty. and like you said, when I looked at the bulkhead it didn't look familiar. Just that point made it easier to walk away from the deal.

So now back to work on these remaining three wires. As I understand some of the diagrams... The remaining Brown is 12v power... The Tan is Ignition.... and The Black / White stripe is ground... Fingers crossed that I don't BarBQ my ECM

[57ToyBox]

UPDATE :
To bring you up to speed. I was converting an 86 cab to work with a TBI engine.
Basically turning a 86 cab into an 87 cab.
Well first I tried to add the wires needed to power the computer for the TBI.
Well I failed at that.
So I found a doner 87 chev truck. I took all the electrical out and switched it over to my cab.
In this process I learned my 305 TBI was garbage (Seized) .
A good friend stepped up and gave me a deal on a 350 TBI

For a couple of days I could NOT get this 350 started... First I though I missed something in the wiring process. Then I thought I had a bad Neutral Safety Switch or it was out of adjustment.
Then I thought I had a bad Starter or solenoid.
Turned out my battery was making 12 VDC but it didn't have the punch needed to start the engine.
New battery w/800 cranking Amps made my awesome 350 purr like a kitten