1990 Series 3 XJ12 - Fuel Injection Harness Removal

I’m doing an LS swap into a 1990 Series 3 XJ12 and I want to remove the original EFI harness. Under the back seat the harness disappears into the body. I’ve Googled and searched forums, but I can’t seem to find out how this harness is routed. Hopefully someone on this forum can shed some light on this.

Best regards

Forward or back? forward should be along the tunnel, and why the engine swap?

Thanks for the tip, I’ll remove the console and see if I can find it.

I purchased the car without the engine and transmission. The car had a V12 with a cracked block and had been sent to be parted out. The underside of the chassis is rust free, and I felt this was the best way to save the car.

I’ve built up a 6L LS (Iron block/Aluminum heads) with new rings, bearing, seals, valves, valve springs, Howard ASA Cam, LS6 intake and Drive By Wire throttle body. The EFI system will be all GM GEN3 electronics. This engine is being mated to a performance built 4L60E.

I’m currently finishing up the rebuild on the front and rear suspension, and I’ve also upgraded the rear gear ratio.


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The harness enters the cabin at the RH footboard, drops down a bit, runs on the floor alongside the console, into the body under the rear seat, and then thru the rear bulkhead into the trunk.

I’ve done a full FI harness remove/replace on a Series III. It’s no joke… if you wanna keep everything intact :slight_smile:

engine harness


Thanks for the help Doug

I cut mine off in the cabin. Only to find that I needed the fuel pump wire. I replaced it and taped off the stub.

Andrew Weinberg of Jaguar-Specialties has a web site with lots of Ls swap information.,

Good guy and posts here from time to time

You might get more action in the Lumpp forum.

Looking at the schematics I noticed the fuel pump wire is in the EFI harness. I’ll be adding a new fuse/relay block in the engine compartment and I’m running new wires for the fuel pump.