I would like to know how the BFU's work. My warning light goes on for several seconds every time I turn on the lights, and then goes off.


On another thread (dormant for 2 years) someone said their pre-facelift system was designed that way. The warning light goes on for about 30 - 45 seconds, and then goes out. They said the units use a bi-metal element that heats up, causing it to bend and that opens contact.


If that is correct, then it makes sense that the light would go on for a period of time. And, perhaps poor contacts in one or more places in the circuits might make the heat up time longer.


My XJS is post-facelift '93.


Thanks,
Greg

 

That is correct. The BFU goes on for 30 seconds or so, then goes out, when you switch on the lights. It proves the system is working, and, as you say, probably is a feature of the design. Also, with the handbrake on, pressing the brake pedal should make the BFU light, as a test it is working.
Greg

 

Another thing to watch out for is the LED upgrade some people are adding to their cars. They don't consume enough current draw to heat up the bulb failure unit to turn it off. Less current is a good thing for Lucas Prince of Darkness. But that is negated with the required installation of a load resistor so your bulb failure unit will operate correctly, but if a single LED fails will it be enough of a difference to keep the bulb failure unit illuminated?

 

Thanks for confirming that. One less electrical glitch to worry about.

 

I probably won't bother spending money on LED's for my external lights. I probably will rarely drive after dark (it's not my daily driver). I did put LED's in my warning cluster to get them visible during daylight with the top down. But that's probably as far as I will go with that type of upgrade.


Thanks,
Greg