Hello, today I upgraded the water pump for the intercooler on my XJR, which is working like a dream now. It feels so much more responsive , I wonder if the old one was working at all.

However when I test drove the car, very time I pressed the break pedal, the bulb failure warning would come on.
All other lights work, it is only the break lights which have failed

I didn't think too much of this as I guessed one bulb was out and I would change it at the end of the test drive. When I went to check I found that BOTH break lights had failed.
I check and changed fuse 6 ((10A (it didn't seem blown)) on the RH healboard but it made no difference

Whilst changing the pump I had been messing around the LH engine relay area, but these are Fog/Starter/Heater pump/Dip/Horn and wiper so I can't see how these would effect the break lights.
I haven't changed the bulbs yet because I can't see how both would fail simultaneously but this will be my first port of call in the morning when its light .

Any pointers would be grateful received.
Thank you,
Peter

 

Put a piece of tape on the voltage gauge and mark to see if it has dropped from when you have the cooler pump fuse in or out

The vnew pump may have dropped the voltage enough to where the current sensors are triggered when you hit the brakes

Blown bulbs would mean a spike in voltage

But then it might just be coincidence

 

Thank you Lady P.
This is a little odd.
I had to take car this morning to have Alloy wheels reconditioned (looked lovely from outside but inner surface very corroded), so didn’t have much time but did change one bulb on LH side. The darn warming light went out!
Last night nether bulb worked!
Now I couldn’t check that they were working, and won’t till I get car back on Wednesday but if the warning light has gone out........
I will update again Wednesday

 

Swap the LH engine fuse box relay with the trunk fuse box relay

The trunk relay may be floating and the LH engine relay in reality is only the horn relay

On page 32 these 5 fuse box relays I refer to as king relays enable power to the 5 points on the car

See page 34 you will see the fuses in that fuse box are not feed by the relay and are hot at all times

On page 38 the trunk fuse box relay ( Ignition positive relay ) must be closed for power to go though a small group of fuses

Page 112 is your brake lights

http://www.jagrepair.com/images/Auto.../jagxj1996.pdf

The actual brake pedal switch has had problems and is replaced with a upgraded switch

http://www.jagrepair.com/images/TSB/...l%20Switch.pdf

Editing

 

Thank you Lady P, will do on Wednesday !

 

Still working on the edit throughout the day

 

Than you so much for your efforts Lady P.
I have been unable to reproduce the problem, (even swapped to bulbs back and lots of wiggle) , but have swapped the relays as you suggested in the hope that this was the problem (intermittent) and won’t happen again!

I am now driving around with gorgeous looking, and more importantly, balanced wheels AND working brake lights!

Oh, and a cool working intercooler.

Thank you again for your efforts, they are appreciated....

Peter

 

I never got back to editing the post deeper

Let me know if the issue returns and will get deeper