It seems the wiring harness from XJ40 models are one of it's weak points. The wiring is fragile in certain places and the insulation seems to be falling off in others. I've worked on many other makes/models of the same era and some cars that were quite a bit older,but the harnesses on these cars appear to be manufactured using cheaper quality materials.Even the wiring in a Series III seems to hold up better. Is there anyone out there making a replacement engine harness for the XJ40?

 

That's really curious. I haven't noticed any insulation becoming fragile on our '93. Was this deterioration on a circuit that had overheated?

The electrical connectors definitely harden and become brittle, but that's a common problem on all the older cars I've worked on. Since the harnesses and connectors in the XJ40 were made by companies like Amphenol and Molex, major manufacturers who sell to virtually the entire auto industry, I don't have any reason to think they are of lower quality than those on other vehicles from the late '80s and early '90s. They are definitely made of thinner plastic than those on earlier cars, but that was likely a part of the overall weight-saving emphasis that was part of the XJ40 design (and automotive engineering in general since CAFE standards were first enacted in response to the oil embargo of the '70s).

One thing that is different about the XJ40 is that the electrical and electronic systems are mostly activated by switching grounds rather than switching power circuits. This allowed the use of lighter-gauge wire in many circuits and supposedly saved a lot of weight.

I'll be curious to hear what other owners report.

Cheers,

Don

 

There are areas of my engine compartment harness,both close to the engine and along the inner fenderwell,where the wire is actually showing signs of cracking. It could possibly be from the fact that I live in South Florida where it's above 70*F about 85% of the time but I've seen and worked on many other cars and have never come across this issue. It almost seems as if the harness is dry rotted like a tire.

 

That stinks. Maybe the hot Florida sun makes the underhood temps especially high? Our car spent the first half of its life in Indiana and the last 19 years in Tennessee. We definitely get some summer heat and humidity but not as brutal as southern Florida.

I recall an episode of Wheeler Dealers in which Mike visited a shop in England that makes custom wiring harnesses, but it was a pretty expensive process. Your best bet would probably be to source a good harness from a salvaged car.

 

I've got a complete pair of spare harnesses from my 94 parts car, big and heavy & in great shape but probably way different to your '88

Was quite the job to get them out without cutting anything.

Back in 1983, made a complete harness for my old TR6 - compared to the XJ40 harness, that TR6 wiring was meat and potatoes ...and of course it just used regular ol' off the shelf/radio shack connectors ...

Larry