As I was driving down the freeway right now at 70 miles an hour in the rain my Xj12 lost all power all I have is lights and windows and that is it, no radio nothing no instrument cluster nothing.
What the hell happend? Any ideas.
While I wait for the tow truck.

 

Thanks to Sarcs help. I have located the ignition relay and was able to tape it together to get ignition and start the car and drive but that doesn't seem to be the full problem.
I've noticed that I don't have low and high beam headlight control.
And I'm getting a fuse 2 error but all of the fuses seem to be okay

 

Been down that (stopped on)road before,NO FUN!Now I always pack a cheap test light in the car,spare relay,paper clips,bits of wire,etc.

To me,it sounds like loose major electric,battery cable or something.
Bang in the road?
Hopefully will be ideas soon
Good luck!

 

Check alternator output and check grounds and battery under load.

 

one of the blue 3amp fuses was blown.
I can't believe that fuse caused all those issues.

 

fuse A5
doesn't say this on the fuse panel.
but in the v12 manual
says
lighting logic
ignition on relay !!!
radio memory

 

So are you back in business ?

It sounds like the ignition relay went haywire and shorted out, blowing the fuse...........

 

yep all is good.
thanks for your always mountain of help

 

I could say that you probably knocked or damaged the relay when you fitted your stereo, but that would just be cruel stone throwing due to V12 jealousy on my part :-)