Hi, I am currently making a new EFI harness for my '85 XJ 4.2L. There is a white with black stripe wire that has a bullet connector joint that is on the side of the head that goes to the ECU to trigger the injectors. This cable is listed as a co-axial cable. Can anyone tell me why it's is coaxial and whether it actually needs to be coaxial? The way I always thought of coaxial wire is a centre wire that carries a signal and another conductor (either wire or aluminium), separated from the centre wire by some sort of plastic, that is earthed. The idea was that the shield would stop any interference and channel it to earth. Now, the coaxial in the Jaguar carries a signal and the so call shield does what? It is not connected to earth, in fact I am not even sure that the wire has a shield, it is very thin. Can anyone shed any light on this wire? Has anyone just replaced it with normal wire with or without repercussions? I can probably source shielded light gauge wire from somewhere to replace the old wire but if it is not really needed I am happy to just replace it with normal wire.
Thanks
Con

 

On the V12 cars (which use the same ignition module, it's a GM 4 pin HEI module) the wire from the coil negative terminal on the module back to the ECU is shielded, that's a RPM signal to the ECU.

Note that the shield is grounded at one end only, that's important. I forget why, but an Electrical Engineer told me that was critical.

 

Thanks Jagboi. I'll open the amp up when I get a chance and check out that end of the cable.
Con

 

Where is it listed as coaxial? It's been a few years but I really don't remember that wire being coaxial on any of the XJ6s I've owned or worked on. The S57 wiring manual doesn't show it as being coax.

Cheers
DD

 

Maybe we're not talking about the same wire. The white/black one I'm thinking of goes from the coil to the ECU pin #1.

The white/black from the amp to the coil might be shielded. I just don't remember

Cheers
DD

 

Doug I think you are right. That is the wire I am referring to as well. I have seen it referred to co-ax and just could not work out why it was called that, as it definately looks like normal wire. In fact there is a thread on JL at present where it is called co-ax. So that answers my question mostly, when I put that wire into my harness it is ok as a normal wire.
Thanks
Con