Where to begin. I have this intermittent fault occurring pretty constantly now when auto lights are active and trying to start the XJR. No crank and rear bulb failure message. Turn the light off crank and start. Turn lights back on and foot on the brake. . . Interlock inop. Turn lights back off, allows vehicle into gear. . lights back on. All seems fine then I notice esp and pass side heated seat back lights are out. 20 minutes or so later back lights are now lit. Really strange stuff. Now if i keep trying to Key the car with the lights on, the security and locking module will trip out. At the point, no crank no matter what, cant lock the car properly, no interlock. Only fix is the walk away and let the car sleep.
So things ive done so far. All the grounds that i know off, cleaned thoroughly, connectors at brake lights checked, connector at body processor module and security locking module checked. My thought is scp network glitch. Any thoughts from the community would be appreciated. 98 XJR.

 

As generic as this sounds, I'd start with getting OBDII codes read.

 

Sorry, forgot to mention no codes. I was getting scp faults a long time ago, but nothing recent.

 

I'd suspect a body control module

 

I'd try a hard reset next. Marginal batteries do weird things like this also. When was the battery put in?

 

The battery could be low, no matter what it's age. Give it a overnight charge and see what happens. It would be a good idea to stop at a parts store and have them do a load test.

 

Yes indeed, low voltage can cause all sorts of stuff. Battery is solid. Wipers also intermittently trigger at random while the car is running, but I think I have a bad Park switch. Just went out and checked b+ with the ignition on lights on 11.98v which doesnt seem like an excessive voltage drop.

 

Any problems with the alarm? remote lock unlock? I had similar issues as you and it turned out to be the BCM.

 

only when provoked lol. If I persist with trying to start the car lights will flash and car will not respond to lock and unlock. Also may be unrelated: I have it set up to auto re arm and since setting it up the error beep occurs after unlock.