My new 1986 XJS has been sitting for 4 weeks as I try and sort out some problems. I have no idea what repairs/fixes have been done prior. I was not getting power to the wipers. I replaced the fuse causing the the fuse to slowly melt away and the plastic of the fuse box to melt. I then replaced the load relay. There had been a 4 post relay not the 5 post required. I started it up and tried to put it in gear. The starter would kick on when I put it in reverse. Disconnected everything. Another relay installed. This time it went into gear without kicking on the starter but smoke started coming out of the dash. Ground and ignition wire to the relay were melting. I compared the wiring into the relay with an electrical diagram. Ignition and ground were both going into 87 post. Black and white wires were in the 85/86 posts. I changed the wires to black/whites on the 87's and the ground and ignition wire to 85, 86. (I believe correct according to the diagram). Started, no melting wires, starter did not engage in gear. Turned it off and then tried to restart. Won't start, starter won't engage. I also still do not have power to the wipers. Any ideas and tips would be appreciated.

 

If this were me, I think I'd disconnect the battery, pull the harness and relays and replace them. A big job, but one that would eliminate all your problems. What started out as a possible short may have damaged more wires and you won't know what/where the damage is until you've pulled the harness.