1992 Facelift 5.3 Engine Wiring Harness Rebuild

I’m rebuilding the engine wiring harness.

Original was very brittle. Car was running okay (after some work), except it was giving me FF34 after test driving it on the interstate and then sitting at idle shortly after. I pulled the injectors and one wasn’t clicking.

I was cleaning up the vee which led to this harness rebuild. Every time I touched the harness it would fall apart. If it was working before it certainly wouldn’t now. As you know, the injector harness is wrapped together with a lot of other wiring in the engine bay. The power module/ignition coil wiring wasn’t in any better shape.

Whatever they used to tape these splices did not age well:

So now the wiring harness has been pulled out, cut off near the boot that leads to the passenger footwell to the various ECUs.

It actually seems pretty straightforward once you have everything unwrapped and start separating the discrete pieces. Easiest one to separate is the Fuel injector harness (makes you seriously question why this was wrapped with the whole harness). Once you split up the 9-way connector there are a few more that can be separated - Oil pressure switch and transmitter is an easy two wire standalone section.

A couple of questions though. I’ve searched around on the forum but didn’t come up with anything.

What is going on here, some sort of diode, but anyone have specifics?

This one by A coil:

This one by the AC Compressor:

What was the idea behind mounting the power modules on the radiator support, do the aluminum plates serve as heat sinks and they put them there for airflow?

I stripped off that yellowed plastic sleeve, and it is a diode!

It is IN4006 and can be found if searched.

I can’t recall coming across two of them, but if you open them up, you’ll find out!

Thank you. I realized I didn’t put the car specs in the title, but you probably deduced that it was a 5.3 L.

I did not. Selfishly, I see facelift, and I assume AJ16

I see the other one now. It is a resistor between the ignition coil and the tach. I was following the wrong white wire, not sure how I missed it.

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Thoughts on wattage for the resistor? 1/8, 1/4, 1/2, or 1w in stock locally.


And from what I understand it is okay to use 1n4007 in place of the 1n4006 diode.

Heatsink indeed, but the problem is the aluminium plates corrode underneath so very little contact to the rest of the car. Take of, clean and reattach (possibly with some thermal paste for full effect).

I’m liking thid but where will you get all the colourfully colour-coded wires from?

Yup, 4007 is the same just 700v reverse voltage prptection instead of 4006s 580v. Forward drop is then same, everything is the same.

I’ve got gxl wire in a variety of colors. Colored heat shrink or I have 3m ScotchCode wire marking tape for the secondary color that I’ll use at each end.


It looks like the PO might have already had some thermal paste on the power modules, but I’ll clean up and reassemble with fresh. The reason I asked was I was thinking of relocating these just because they are kind of out of the way and I was looking to reduce the the length of wiring. I’ll leave them there for access to airflow and probably reroute the wires along the right fender instead of right above the exhaust manifold.

Thoughts on wrapping?

Demonstrated here on a very easy part of the harness to split off from the rest - fuel rail temperature sender. Wires heading along the fuel rail to the rear bulkhead. I’ll terminate with a 2-way weather pack replacing the 4-way green sumitomo (the other two into this connector are the shielded wire connecting the efi ecu/diagnostic socket/ground and the ignition ecu. Someone tell me why they decided to make that connection in the engine bay. That connection will get its own 2-way, I think.)

On to the choices:

Expendable braided (I have a lot of this in a few different sizes). I’d use adhesive heat shrink tubing at the ends.

The split tube variety (again, I have a lot of this, but only two sizes; the one shown here and some larger stuff)

Harness tape (I just have a small roll. Might not be cost effective)

Silicone braided sleeve (don’t have, but not that expensive)

Heat shrink tubing (I may actually have enough for this harness. It is mostly adhesive, so future work might be a pain. Picture is unshrinked.)

Any other suggestions?

My vote for looks goes to the braid as it’s the most modern. My vote for function and protection would definitely NOT go to braid because it provides exactly zero protection, I would even go so far as to drip a bit of fuel, see if it melts?

What I have done is use the non-sealed heat shrink and only shrink it with heat at the ends- that way it can still flex as the wires can still slide inside of it.
Harness tape would be best for areas not prone to abrasion; a lot of current vehicles use this with only 50% of the harness covered. Saves material and cost. I used it a little differently, overlapping each wrap about 25%. It has no adhesive so harness is flexible (especially the way the OEMs use it). Just super glue the wrap at the start and finish of the wrap and only glue it to itself. This allows easiest branch offs.
Never use vinyl electric tape; harness becomes rigid and a sticky mess with oil or heat, and then the adhesive fails.

The expandable braided sleeve is polyester, so at least somewhat resistant to gas. Flame retardant and good up to 125 degrees Celsius.

Went ahead and finished that one with the braided. I think it looks pretty good.

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As I said, braid looks the best. But also as I said not sure what protection all those holes in the braid offer? In the first picture of the braid and cable you posted up there the braid is see-through towards the ends. But if the cable you’re using has good enough material for isolation then the braid is just cosmetic in which case go with braid.

I’m working in the EFI portion now. There’sa but of discrepancy between the diagram and how the car was actually wired.

The diagram shows 1,2, & 3 (orange/blue on bank A) grouped together and 4, 5, & 6 (orange/white) grouped together.

How the car was wired was alternating injectors grouped together 1, 3, & 5 (OU) and 2, 4, & 6 (OW)

I’m guessing I should wire to how the car was wired not according to the diagram.


I guess the alternating grouping matches what @V12JagGuy posted:


There is a discrepancy on one year’s diagram. I don’t know why. It doesn’t really matter because the two channels for each bank are fused in the ECU so they actually fire in bank to bank batch as if the ECU only had one channel per bank.

~Paul K.

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Thank you, Paul, for the clarification. I see the section in the ROM and the Book that describes these groupings.

I was going off the 1992 MY Electrical Guide - looked up other years and, yes, seems like '92 there was a typo.




No problem.

Take another look at the 90-91 diagram. It’s ok. The injectors are in order, but note the connections are staggered. I think it was only the 92’ year that had the strange diagram.

Actually you’re exp is the first time that I know if that confirms the diagram is wrong. All other factors indicated such (no change in harness part number, — surrounding years being shown wired the same - staggered)…

See how 2, 4, and 6 are on one connection, and 1, 3, and 5 are on another?

Again, if you got it wrong, it’d be ok since they’re fired bank to bank. I’m guessing that if a connection went out, the engine would still run a bit more balanced on that 9 cylinders than just on 6 on one side and 3 in the back or front of the other? IDK.