I am helping a friend who is the new owner of an '86 XJS which is suffering numerous electrical issues. While I imagine I may post on other subjects, I think it best to stick to one issue per thread.

Vehicle particulars:
'86, 5.3L, US spec with manual seatbelts and factory trip computer.

I have been referencing the factory service manual, which includes two addendums. In total, there are about three wiring diagrams, however through a great deal of effort I hve determined the brake ligt circuit of this 1986 XJS appears to match the wiring diagram la bled for 1988 1/2 model year. Go figure.

This version of the brake light circuit sources 12V through the brake switch directly to the stomp lamp failure detection module. The brake light switch has Green and a Green/Purple wires. 12V comes to the Green wire by way of a fuse. I believe this fuse to be the culprit as there is no 12V on the green wire and applying 12V to the Green/Purple activates the stop lamps. My problem is, I cannot locate this fuse.

Other circuit configurations indicate the #5 fuse as the source of power for the stop lamp circuit, but this configuration references fuse "86". My belief is this must be an inline fuse somewhere, but I have looked and looked and cannot find such a fuse. According to the diagram, it should have one gGreen wire and one White/pinK wire.

Anyhelp in locating this wayward fuse would be greatly appreciated.

Submitted by leodelc@comcast.net on Mon, 01/09/2006 - 02:40

I measured 12V on both sides of the fuse. I also checked for continuity, and found none. I am not ruling out an issue with the fuse block itself; I tried unmounting it to check the wiring, but there is zero slack and I was unable to get it to move enough to inspect the wire terminations.

In the diagram I am looking at, there are G and GP wires on the switch, and it is switching to +12V. Other variations I have seen in this book have differnt wire colors, both for this switch and for the "error detection module". The wire colors for both switch and module match 100%, and it shows a single fuse (85) with G and WK wires.

Submitted by dougdwyer@adel… on Mon, 01/09/2006 - 00:56

I have diagrams for '76 thru '91. They all show fuse #5, and no inline fuse, for the brake lamps.

Have you checked the #5 fuse? Better yet, simply replaced it ? Are the fuse clips clean and snug ?

Doug Dwyer
Longview Washington USA
1987 XJ6 Ser III
1988 XJS V12 Coupe