I'm in desperate need of help, can somebody please tell me and show me where this broken white wire is supposed to connect to? It's Wire number 24 on the Marelli ignition module.

Thank you

 

Someone please I'm stranded

 

Near as I can tell it ultimately goes to pin 18 of the fuel injection ECU. The diagram is a bit vague.

But if it's broken you should see the other end dangling around there somewhere.

Cheers
DD

 

Doug is correct pin 18 on the Marelli goes to pin 24 on the Lucas ECU. Without this wire the ECU will not fire the injectors, This is the Tach wire that tells the ECU the engine is turning. Looks to me someone has been there before you with the wire splice.

Are you sure there is no continuity between pins 18 & 24, check it with a meter with both connectors disconnected from their ECU's

 

I tried to find the wire that was dangling to where connects to but I can find anything. Is it possible I could splice the wire and run it alongside the vehicle to the trunk to Pin 18 of the FI ecu?

 

Lets stop for a minute and can you describe your problem in detail. Because at the moment we are trying to help you find a problem and I do not know what that problem is.

Does your car start or does it just crank etc?

Yes that wire goes to pin 18 of the Lucas but where does that Black wire go? Someone has been here before and might have repaired this and you are chasing a problem that does not exist here.

 

I have just come through building a whole new ignition harness for my Marelli car. Pin 24 goes to the EFI unit for sure. But you can find that white wire where where the main harness passes through the fender going to the rear of the car. It is coax wire. I bought some 59R coax from a local electronics supply store. It has stranded center, which is supposed to be in a automotive application. There is a great reference guide for every year on Jaguar electrical reference

I agree about wondering what your original problem was, taking you to this part of your harness. Feel free to contact me if I can be of any help. My car was a non running mess when I bought it, and only after asking lots of questions, doing lots of research, did I finally get a handle on the Marelli system, and now have the car running great. I put weatherpac connectors everywhere the harness was grafted into Lucas, just in case I ever wanted to take the Marelli harness out individually, without cutting anything.

 

The coax should be grounded at the Lucas ECU ONLY, the Marelli end shield should be left unconnected. It might not cause issues immediately but will be prone to noise if it is grounded at both ends.

You need to remove the white wire so it does not short on anything.

 

The problem I'm having is:

The car will start for about 30secs but will shake violently then die, tests fuel pressure (good) but very weak injector pulse all around. That's when I found that white wire dangling. This all happened a few days after I replaced a few cables from the harness. The was running good after i replaced the wires. Something happened its frustrating not being able to figure it out. Wish there was a detailed diagram for each wire and where it goes. Please help. It's been over 2 months of a non running car..

 

http://www.captainjaguarscathouse.co...ec%20Guide.pdf

If you look at the wiring diagram for a 89 XJS on www.captjaguarscathouse.com, scroll to the next to the last diagram, 29.1, and it is about as detailed as you could ask for. Pin 24 is the Lucas ECU wire. The whole harness will come up through the firewall with a little effort. I used this diagram to completely hand build my new harness. I'm not sure about NOT ground the wire as suggested by Warren. I did, and don't have any noise. BUT, this is NOT a shielded wire as described in the wiring diagram. It is automotive coax. Really not hard at all to work with, splice, if you are decent with a soldering gun. The other end of this wire IS in the harness. It passes through the fender, in with the main harness. If you need to call, send me a private email, and I'll send you my phone number. Glad to help, as I got plenty of help getting my car running. I bought mine not running, with no idea of why, or anything. Never had worked with a car with Marelli either.

 

Btw, not sure about someone being there before, other than maybe the person on the assembly line. The Lucas ECU harness has nothing to do with the Marelli harness, except for THAT wire. The tach wire is spliced in onto the A side coil wire up in the valley. I can imagine that as these cars were assembled, some splicing HAD to occur.