Fail safe mode, I know this has been reported before :( 1999 XJR resolved!

Normally I would say brake light switch on the pedal but I have just replace the micro switches with new items and confirm when I depress the pedal I get the two distinct clicks as they operate.
Now the interesting point is that only the main brake lights illuminate, NOT the high stop, I can confirm the HS comes on with the brake pedal, and I notice there is a very short period where the main brake lights flick off and then back on with the HS. Is there a module I need to be looking at?
UPDATE, turns out it isn’t the brake switch as after a drive where the fault showed up I left the engine running and disconnected the plug to the switch and the main brake lights are still glowing bright :frowning: on the upside the micro switches work :slight_smile:

I’m unclear of your symptoms.

I’d still be looking at the brake switch. Turn the cruise control master switch off, and see if the problem goes away.

If the left or right brake lights are stuck on when parked, that we be a failed FET

Sorry I’ll try to be a bit clearer.
Car starts off normally, i.e. the CC works and the brakes lights are off until the brake pedal is depressed. After about 3 klms the engine fail safe mode pops up the CC cuts out and the main BL remain lit. I observed in a window when parked that as I depressed the brake pedal there was a momentary distinguishing of the main BL then all three will come on. I would mention that I do not notice any difference in the engine response to the throttle. As mentioned disconnecting the brake switch does not kill the main lights when it has faulted.

I’m a bit confused too, but was thinking about the security module under the boot fuse box.

It controls main brake lights, but not the high third.

I had a car where the mains didn’t work, but the high did. It was the security module.

I learned from one of these forums, that the main rear lights go through the security module, so that lights can be illuminated if there’s a break in.

Good luck,

Thanks Rob, had it into the sparkies today and they diagnosed a dodgy alternator, I’m a bit wary of this as when I checked the battery seemed to be receiving an adequate charge, having said that it might be that its leaking back through the alternator. I have a good 2nd hand one that hopefully they can fit tomorrow, sounds like the security module may be the culprit for the brake lights, I wonder if that will also be the cause of the fault on the dash.

Update, should have the car back from the auto electricians by mid week.
The brake and CC problem turned out to be in the body control module. Makes sense as its in the engine compartment on the same side that took the majority of the damage when I fell off the road during last years Targa Tour.