Over the years I drew up a number of diagrams to help me build harnesses. Since I am no longer doing that, it seems they would be more useful here. Bear in mind, I drew these as an aid for myself and may have an error or two. Quite a few of these are simply redrawn for clarity as most GM and Holley schematics give me eye cancer

I apologize for the poor resolution. Not everything picks up well on a screenshot. If someone wishes to convert this .DWG to a higher resolution image, please contact me

All diagrams will be first posted with an easy to read white on black, then a printer friendly black on white at the end

Lets start with the C100/C207 connectors and what's needed for a swap. Omitted wires aren't used EX: 90-92 TBI cars pass VSS wires through the C100

EFI cars are pretty straitforward






Carb cars require a fuseblock be added on. Hard to read, but the jist is the same as 85-87 cars plus a fuseblock





Printer versions

 

Fuseblock and AC diagrams. AC can be controlled via PCM or independent. Factory 94-97 LT1 and 98-02 LS1 have the option for PCM control. Other systems should be wired independently. Anything R4, sanden, holley etc should be ran independent



Basic fuselbock





More inclusive fuseblock

 

ECM/PCM diagrams

 

Trans controls and detail of the pedal diagram from the ECM schematics. Compatible pedal PNs and which wires switched between them

 

6L80E/6L90E

 

Oddball 98 LS1

 

Finally,the holley stuff. These are holley diagrams redrawn for clarity and have the colors changed to the more familiar GM LS. When I grab a random connector, I identify it by wire color/qty. LT GRN, GRY and BLK are MAP for basically anything GM. Holley uses RED/BLK, ORN, BLK/WHT, which is confusing

24x



58x



Trans control
Holley uses a large relay to disconnect the 12v IGN for the trans. If you're building your own harness or adding a fuseblock, then the IGN to the trans REQUIRES A DIODE. Direct 12v IGN will backfeed to the ECU causing a 'no shutdown'. Symptoms: no shutdown, scrambled handheld screen, 6-8v on the circuit key off. In this case, pull the main 40A fuse to the ECU, or unplug the main power connector. Do not leave the ECU powered up like this for long. It does NOT like low voltage situations




09+ 4L60E's have a unique pinout



DBW












Hope these are helpful. God bless

 

Thank you!

 

thank you sir!

sticky worthy!

 

What parts and tools did you use to make the multi-wire splice for common grounds?

I have never been able to find a long crimp splice like GM used.

 

I solder multi-wire splices. Crimps are fine if done right, but I've replaced a bunch of bad ones. If you plan out solder splice locations or simply loop them, then fracture isn't a concern

 

Where did you buy your wire from?

Your schematics already unlocked one the mysteries that was stalling me out on my own project. Easy pleasy now!

 

What mystery is that?

I buy my wire from waytek

 

The Holley 4-wire CAN vs. my older harness with 2-wire CAN. Now I see the CAN network is actually still the same, and the extra two wires are power and ground for other hardware.

 

Yeah, simple IGN/grd. I prefer to use the same IGN source as what goes to the ECU
Strange how holley splices the grd leg into whatever they feel like. LS 24x/58x are in the CRK/CAM circuit, SBC and Coyote all use different pins at the ECU. Holley dominator instructions say to use an external grd. Without knowing the inner workings of the ECU, I just match what their diagrams dictate

Also, I absolutely despise that little CAN connector. For most builds, I tee the two can wires and hard solder them to a laptop cable. The original CAN is present for any accy (handheld, dash, etc) and the laptop cable has far less connection issues. No more ripping your thumbnail off trying to separate them




One last big one I forgot to add to the Holley trans stuff:

The IGN going to the trans connector for 4L60E/80E's REQUIRE A DIODE or it will back feed to the ECU and cause a 'no shutdown' situation. Holley uses a giant Hella relay to accomplish this. If you're building a board, just add a diode

 

This post messed with my mind.

I know I used the same word combo to search if this info was out here! It wasn't then. Looking at the date, this was posted shortly after i completed mine!

Pocket still lives!!!

Heard good things about you pocket! tried to get in touch with you to have you make me a harness. This whole experience grew me into a new love for automotive wiring! Preferably from scratch!

 

Pocket,
Thanks for all your schematics. I wired my fans off your schematics fans aren't coming on. I believe the PCM should start 1 fan at about 228°?
I can start the fans manually through my Snap On Solus scanner. But I'm getting the dreaded P0480 & P0481 codes (coolant fan control circuit) ??
PCM is giving my Scanner an accurate temp so it can't be a temp sender?
I put a jumper wire on one of the Relays and physically grounded it to the battery and fan comes on. So my pcm must be bad??
If I posted this in the wrong place my apologies..

 

What ECM are you running and do you know if the donor vehicle had PWMF or binary fans? If it had pulse width, the fans will not come on with an ECM signal.

 

I am using the ECM from the donor drivetrain (02 Trans Am) What is PWMF?

 

PWM is pulse width modulation. Its basically a fan that can operate under various speeds. The ECM controls it via a voltage range rather than providing a ground in the traditional sense (just on/off). I don't think the 411 ECM's had PWM on their operating system but I could be wrong.

 

I'm pretty sure my ECM is a 411. Weird how I can activate the fans with my scanner 😆

 

Then your ECM is sending a ground signal to the fan relay based on coolant temp reading.

 

then I don't think so have a bad PCM?? I wonder why I'm getting codes P0480 & P0481??
I guess I might have to get to a tuner sooner than I thought. I was gonna grab another PCM and try it out first. Thanks for your help...

 

Delete dreaded trouble codes with my Solus Scanner. Disconnect battery for 15 minutes.
Re-attach positive battery cable and fire up. Let it idle till it gets to 225° and miraculously fan comes on. I love when cars fix themselves.
Ice cold Banquet Beer and the humming of 87 IROC-Z fans. Life is good. 😉