[Nysil Via]

I made the new harness and tested it this weekend. It works.

Here is the new harness compared to the old harness. I started with a wiring specialties replacement harness. The big problem with doing using the Wiring Specialties harness is that the loop for the timing light won't work. At least I don't think it will as it becomes a low voltage wire in the new harness.

Below is how I modified the connectors to account for the space issue that was noted. the top row is the unmodified connector, and the bottom row is the modified version. Obviously the modification should take place while the connector is depinned.

and here is the first pic with a crop zoom so you can get an idea of the space it creates

As for the wiring,

The stock system has one wire from the main harness and split to the four coils that provides 12-14V. This wire is white on cylinders 2-4 and Black with a yellow stripe for cylinder 1. Each cylinder also has a Black ground that is spliced together to the eyelet connector that gets bolted to the head. And finally there are three red wires with colored stripes for cylinders 2-4 and one black wire for cylinder 1. these last four wires individually go to the connector that connects to the main harness, and brings those four wires to the ignitor chip.

The ignitor chip is a device that takes in a low voltage signal from the ECU and completes the ground connection on the 12V circuit to that coil. What you will need is an ignitor chip bypass that will send the ECU signal all the way up to the new GM coils. Then you need to wire in a second ground wire into the harness.

if you look at my picture that shows the connector mod, you can see on the bottom side of the connector, ther eare the numbers 1 and 4. these are pin labels.

Pin 1 - Head Ground. This is the same head ground wire on the stock harness. Black wires in my picture

Pin 2 - Chassis ground. These are the wires that need to be added. Blue wires in my picture

Pin 3 - ECU signal. there are the wires that have to get pinned to the right location on the harness connector because they go to the ignitor chip bypass. these become the signal wires. Red in my picture

Pin 4 - 12V-14V supply from the main harness, these get spliced to one wire and that one wire has to be pinned to the right location in the harness connector. White in my picture.

Additional information.

I was fortunate to be able to find the cois with the harness and the needed connectors. but if you need to source the connectors on your own, they are
Molex 33471-0461. The pins are Molex 33012-something depending on the wire gauge you are using.