Just purchased a 98 xjr with 70000m on it . Battery is being drained by a small fan that looks like a pc fan i unplugged it for now any ideas on what this fan does i think its to cool the ecu and y it would stay on besides the possible short ? I will post if i find anything

 

There is indeed a PC fan to cool the ECM/TCM fed off fuse 16 in the Engine Management Fuse Box. All the fuses are ignition switched power fed from the ECM control relay and then from the ignition switch. I would verify that the relay is operating correctly and not stuck operated. All the relays in that box are the same and can be swapped. If that is not the problem you will need to look at the ignition switch to ensure it is dropping power when in the off position.

The FAQ sticky above has the JTIS download which contains all the schematics for your car.

. . . and welcome to the forum!