I've been working through all the issues the 1994 X300 XJR I bought last month has and I've hit a brick wall with one of them.

The rear fog lights refuse to work despite fitting new (second hand) switch pack on dash and rear light ECU. I've also repaired the rear loom which had breaks in it due to a previous owner splicing into it to fit a by pass switch to operate them.

I've checked the fuses, in the rear fuse box and the L/H rear passenger foot well as I have a handbook which conflicts with the wiring diagram, the loom from the dash switch to the rear ECU and from the rear ECU to the lights themselves and all seems OK. When you earth the wires going to the rear fogs with the dash switch in the on position it lights up and so do the fogs.

Can anyone suggest where i might look to cure this problem.

Thanks Woodworkwilly

 

By rear fog lights is that the red at night running lights other then the red brake lights ?

Going off line

 

Hi Lady P, no its the lights which are operated by the switch next to the boot release switch.

 

I take it you are allowing for the fact that the fogs will only operate when the headlights are on?
From the rest of what you have said, have you checked the fogs are earthed? I dont have the wiring diagram to hand, but from your comment that they work when you give them an earth, there would seem to be a suggestion that that is what is missing. Bear in mind the wiring uses switched earths as well as switched positives, so the wiring diagram is your friend...

 

It's been a while since I worked on the rear fog light circuits but I believe the BPM is involved.

bob

 

Switch " B " ? The early X300 series has 2 lamp control modules and the later has 1 . This is other then the interior illumination module . Looking at the year difference but my copy of the 1995 wiring guide does not allow me to take a snapshot for a pic of the page .

1994.5 - 95 uses fuse # 9 / 15 amp Trunk fuse box and fuse # 2 / 5 amp RH heelboard fuse box with the rear lighting control module , ref figure 9.3 in the 1995 wiring guide .

For vehicle 739427 on : Uses the same drawing as 1996 , ref figure 9.7 in the 1995 wiring guide .

The wire drawings between the years are functionally the same .

Woodworkwilly , was the tail light lens assembly modified and have the X308 assembly as they do physically fit with the difference I believe the width of the chrome surrounds and bulb count ? If I understand correctly if you give it a external ground path everything works fine ?

The second X308 print below is colored in for a different problem

 

I have replaced all the rear lamps with LEDs. The Brake lamps have added resistors. The lamp failure warning is on all the time.

Is there a work around so I may avoid more resistors?
Thank you for the wiring diagrams Lady Penelope! you are a lifesaver

 

The lamp failure monitor is most likely a current sensor so you must match the current . To high current is OK but not too low before the monitor trips . Zero is a open / failed bulb . LED's are very very low current , 20 milliamps typically as a general rule . You would have to make a circuit running parallel to the LED's after the monitor to carry the needed minimum current .