I have been having the error messages 'Check Rear Lights' and 'Cruise Not Available' for some time now. The problem was correctly diagnosed by members as a faulty Brake Light Switch (thank you members) and confirmed as the likely cause by my local main dealer Grange Jaguar (Exeter). It was annoying but not terminal and it became a game to see how many miles on each journey I could go before brake pedal pressure triggered the fault. With gentle braking it was amazing how far I could get but the problem needed resolving.
Internet research revealed that this 'simple' job was a potential nightmare as replacing the switch was difficult to say the least as access is extremely limited and the solutions although creative seemed to involve hours of effort and two people as more than two hands were necessary both inside the footwell and under the bonnet. My local dealer advised that the Jaguar job time was two hours labour so clearly there was a lot involved to do it the 'standard' way.
I was intrigued by some internet comments made that replacing the switch involved replacing the switch unit which comprised both a bracket and switch unit as a single unit but the two components could be separated without damage to the switch unit. Was it possible to replace the switch unit without the bracket after all the problem is with the switch and not the bracket?
Investigation of the actual brake switch location involves lying on your back and getting your head under the brake pedal. I managed this reasonably easily and I have my bus pass....... What I found was that the switch is hidden behind sound deadening material that has a cut out slot to accomodate for the brake pedal travel. I am not sure if someone had been there before me but the sound deadening material had a couple of transverse cuts enabling a hand to be inserted and the switch could be located on the bracket by feel. Most importantly the two retaining nuts that secured the plastic switch to the bracket could be felt so it seemed possible that replacement of the switch was do-able.
I purchased a replacement switch. This I carefully checked to ensure that removing the plastic switch from the bracket would not present any problems. It doesn't, the two components can be separated very easily without an explosion of springs and components. It also enabled me to check how the nuts could be removed. The lower nut was easily accessible but the upper could only be removed with an 8mm socket as there was not enough clearance to work either a ring or open spanner.
First step was to slice the sound deadening material so that it could be peeled back in four segments and tucked out of the way. This gives sufficient access for one hand and limited visibility of the components. You will need a torch or light of some kind of some kind. I was able to get by with a torch propped against the brake footrest.....
The lower nut was easily accessible and slackening this was possible with an 8mm socket and small 1/4" tommy bar. This obviously was removable but the upper nut was more problematic. I could get the 8mm socket on it but how to turn it? The tommy bar required too much space and there was insufficient space for a flexible drive because of surrounding components and obstacles. Defeat beckoned but stubborness kicked in. If the socket would go on there had to be a way to turn it. I needed a tool that resembled a radiator bleed valve key!
I made up a removal tool using an 8mm socket, part of redundant wardrobe hinge bracket that came to hand from the 'bits' box and araldite.
Installing the new switch was very straightforward, as straightforward as anything is when lying on your back using your 'wrong' hand and only partially sighted ......but not a real problem. It took just a couple of minutes.
With the new switch installed I set off for a road test. All OK. Job done. Reunited the sound deadening material and repaired with gaffa tape. (No problem as this will never be seen by anyone unless they have their head upside down in the driver's footwell).
It took me one and a half hours to do the job. About half an hour to actually do it and an hour to figure out how and make up the 'tool'
So it is possible to change the brake switch on an XK8 single handed (literally as you can't use two) without changing its bracket!
I am now feeling very smug beating a Jaguar design fault!
Mike.