Hello!
After a long hiatus I'm back in the Jaguar game - picked up a neglected '87 XJ6 for next to nothing from the owner of a business who seemed to be moving out. According to the previous owner it's been about a year since it was last run, and it has not been kept well judging by the peeling clear coat and crunchy seats.

Fluids look good, and gas smells fine, so my plan was to drop a new battery in it (there was none), fire it up, and see what needs fixing from there. Lights/warning lights/etc. come on when I turn the key, but there's no crank. I jumped the relay to the starter wire and it cranked just fine, so my first thought was to replace the starter relay. I have one on order, but I began to check other wires in the meantime.
Here's what I found:
Brown wire has 12v constant (I believe this is correct)
Red/White is to the starter (this is the one I jumped)
Blue/White wire...color seems wrong, but I'm guessing this is to the EFI?

White/Yellow Wire - I think this one is supposed to receive power when the key is turned, which trips the relay to provide power from Brown to Red/White, but I did not get power from it when in the crank position. This seems odd to me, as everything else in the car seems to light up as expected when I turn the key, so ignition is getting power. From the wiring diagram, it looks like this white/yellow runs directly to starter relay with intervening relays or fuses (although I did check and all fuses in the 3 fuse boxes check out as good).

Any ideas on what could cause the W/Y wire to not receive power from the ignition switch, when the ignition switch itself is getting power? I will likely replace the starter relay anyway to see if that works (maybe my multimeter connection wasn't as good as I thought), but would appreciate any other ideas!

 

Yes the white/yellow is the trigger wire for the relay. A faulty ignition switch comes to mind...a fairly common fault. But first look around for an alarm system that might be immobilizing the circuit.

Ignore the white/blue wire. It isn't used; it's existence is a slight mystery. I think it pertain to the 3.4 engine cars....but no need to get into the weeds on that

Cheers
DD

 

Definitely seems like the ignition switch - all the wires at the switch are lighting up except for the W/Y when cranked...I will explore repair vs replace and go from there.

From the diagrams, it looks like W/Y from the ignition switch also supplies power to EFI. Is it that the same wire? I'm confused because in the diagram it looks like a second wire, but I don't have a second wire. I guess my question is if I jump the W/Y from the ignition switch, should the car start if everything else is in order?

Thank you!

 

A single white/yellow leaves the ignition switch. Downstream it branches into two, one to the starter relay and the other to the bulb check unit.

From the starter relay the white/yellow continues on the the fuel pump circuit, the cold start circuit, and the ECU, in series. When you turn the key to 'start' all these things get voltage simultaneously. If you apply 12+ to the white/yellow wire the starter should engage and the other items get the voltage they need. Whether or not the engine actually starts is another matter!

Cheers
DD

 

Fair enough! Thank you for the explanation. Turns out the ignition switch wasn't rotating fully. I took it apart and messed around a bit...overall it was very clean. The little spring part shown below seemed to be getting caught up, and I think the solder from spring to "handle" broke when I tried to adjust it. I ended up removing it...I'm not sure what it does but at this point I can get power to Y/W when turning the key, so I will take the dubious step of reinstalling it and seeing if anything else screws up without it.

 

Ok, ignition switch is reinstalled and getting power to W/Y, but that power is still not reaching the starter relay. When I turn the key to crank position, I hear a click (think it's the Load Relay), the parking brake dummy
light comes on, and the brake dummy light blinks. It looks like the leads to the brake reservoir are broken so it’s possible the brake light is unrelated.

Neutral Safety Switch seems fine (black/green into start relay is grounded)

Looks like I have some wire tracing to do...I'm not sure what else can kill the ignition circuit. Thoughts appreciated!

 

So it turns out there is a second W/Y wire coming out of the Starter relay. The one I was testing is actually the connection to the diodes, while the one a bit out of sight was the one I should have been testing. My multimeter registers continuity between W/Y at the ignition switch, and the W/Y at the bulkhead connector, and the bulkhead connector registers continuity to the (I think) correct W/Y at the starter relay. But for some reason I'm not registering continuity all the way from the ignition switch to the relay, and I'm still not seeing significant voltage (I got maybe 1 volt that hung around for a while) when cranking. Not sure if my multimeter is not working correctly, or if I'm doing something wrong. In any case, original wiring seems to be intact and functional. I've ordered a new starter relay, and hopefully that cures what fixing the ignition switch didn't.

May do some additional testing, and open to any thoughts. Hope to have this Jag at least cranking soon.

EDIT: It is NOT the relay - direct power to the correct W/Y (I was jumping the wrong one) does crank, and with a bit of coaxing she fired up, so likely something in the wiring between the ignition switch and the relay. I'll close out this thread for now and post a new one if I run into further issues. Thank you for the education on Jaaaag wiring!