Hello,
I joined the forum, hoping to get help with a problem. I just purchased a beautiful 1993 XJS 4.0 convertible. It has 34K original miles and drives beautifully. I noticed I had no tail lights and found the side-light relay missing. One of those blue Hella relays, ya know? I got a relay, plugged it in and of course, I had tail lights again. All is fine, right? Nope!

When you turn off the engine and you leave the lights on, you get the lights on warning buzzer, so you turn off the lights! That is when you notice the buzzer "chirps" shortly, about every 5 seconds, as the lights give a little flash, all of the lights, headlight, tail light side lights, except the front right side light that is missing that had a bad bulb. I checked the socket on that bulb for power, it had power so I pulled the bad bulb.

So, engine on/lights off = no blink and the lights off.
Engine off/lights off = blink every 5 seconds or so, including bad bulb warning light (because of my bad front right side light) and the warning buzzer in sequence with the flash. ( at least I know the warning buzzer and bad bulb warning light are doing their job)

switch?

Any ideas where the short is and why it pulses every 5 or so seconds when the engine is off but fine with the engine running and the lights off, they are off and do not blink?

 

Mine shows the exact same symptoms. I get the warning buzzer and my tail and instrument panel lights are gone. It started with a delay. lights would turn on after a couple of minutes, but know nothing.

From reading, I think its the side light relay which is like you mention one of the blue ones. Do you know which one. Also a 1996 xjs convertible. going to move them around see what happens.

 

It is the second blue relay from the left, above the left front wheel, under the hood.

Replace that one and you will have your side and tail lights back. Does your car flash the lights for a spit second, every 5 secs or so after you turn off the car?