So when it's on, the light is red?

 

Yes

 

Yes, but I'm talking about the switch that is located under the dash that activates the Brake lights and also cancels the Cruise. Is it LNB6420BB

 

Yes.

Only tricky thing of replacing it is the contortion to get in the space.

If memory serves, the bolt holding it in place is 7mm & is the only time I've ever needed to use a 7 mm wrench.......

 

Went out today and it really acted up. Went into it's Zone again LOL. Even with the lack of a Limp home mode the cruise wouldn't work. The light on the Console was red but wouldn't work. Came home pulled the LF seat, laid on my back & removed the switch. Made my own lubrication holes in both Micro-switches sprayed some CRC 2-26 into the switches, Then took back out on the road and so far so good!?

 

This thread has gone on far too long for what may have been a simple problem. I hope you finally have the solution.

 

Only to far to the one who doesn't own the car....Many thanks to everyone, a great bunch of guys!!

 

I have a 2000 XK8 with 76K.
Don't know if this will help, but here is my tale of woe.
Started getting "ENGINE FAILSAFE MODE" but engine ran fine. Tracked it down to a bad brake switch which I replaced. Have not had "EFM" since
(~500 miles). Engine runs great. Brake lights work, cruise does not. CC switch on console is lit.
Haven't started trouble shooting as its so dog gone cold (in NC!) I suspect it is the brake switch needing adjustment, but I don't see how to adjust looking at the switch and the mounting. I will try cleaning plug contacts first. If the mount for your brake switch is the same as the XK8, it is a bear to replace until you find the secret. (thread on one of the mount studs which allows you to hold the switch in place while you crawl out from under the dash and take a look at how the studs are aligning with the holes. Then back under the dash to get the studs in the holes)

 

I removed mine by taking out the lf seat which had to be done as far as I could see. It was easy to remove just hard to determine the size of nut & bolts. I drilled both Micro-switches and sprayed a Electrical Cleaner inside each hole and so far so good. Yes, your switch may be the problem...