Today I confirmed a fix on a 1996 Jaguar XK8 that had the sidelights permanently on, even when the car was locked, leaving the car unusable as the battery would constantly go flat.

The exterior lights are controlled by the switch, which tells the body control module (BCM) to turn on the lights, which then go through a bulb failure module! Slightly over-complicated!

All of these tested ok, but our diagnostic tool connected to the BCM falsely said that the switch was on. Using the factory wiring diagram I could see that the sidelights also had a link to the dimmer control module! Another one!

Tests proved that this module had failed and was keeping the lights on, which today was cured with the arrival of a new module from Jaguar.

The customer was great all along, he felt confident after talking to me that I could correctly diagnose it if given the required time, which he allowed me, and then when the faulty part was singled out he agreed that a new part was the best way to proceed.

A relatively complex fault to locate, but, for the customer’s outlay, he now has the use of his car back and, as always, no unnecessary parts were fitted.