Gents,
While working on my son's XJR (primary and secondary tensioners),(boy am I glad that's done). I noticed all three of his brake lights were out; left, right and 3rd above. After changing bulbs, checking fuse and relay in the trunk...still the prince of darkness reigns. I am at a loss as to how to proceed to trouble shoot from here. Thoughts of a blown security, locking control module are dancing in my head as Ohm's law continues to laugh at my feeble efforts. Any advice from the group greatly appreciated. Thanks
Also back up lights appear to be functioning normally

 

How about the brake light switch activated by the brake pedal? Common failure but usually shows up as other issues than the lights themselves. There are a number of links on changing the switch found in the stickies above or elsewhere in the forum.

 

were break lights working before you tackled the tensioners....?are you getting any message on the display?......of course the switch is a possibility....but i think a far flung coincidence that they stopped working during/after doing some surgery to the car....

I will scale down a bit...... as per similar incident when adjusting cams on my maxi-scooter. When i removed the shroud to get to the engine i inadvertently disconnected a brake switch/ sensor. After I finished the job, I put everything back together but the bike would not start. I had to take apart again to find what was going on.

Engine would crank but bike would not start. The ecu detects "no brake lights" and therefore no start. On a bike brakes are a critical safety feature (of course important on cars as well), so possibly something you touched/moved related to your upgrade may be whats going on.

 

Thanks Testpoint and Jagjunky. Neglected to point out that the brakelight symptoms were prior to tensioner work. Have not had time as yet to do a deep dive into resolution,but turned on emergency flashers and the left and right brakelights were fully functional. Can I assume the signal coming emergency flashers would be routed the same way to the SLCM as the brakelight switch? If so could I rule out any broken wire on harness at trunk hinge and also faulty SLCM? If all the above is true, me thinks brakelight switch as per testlights suggestion. Can someone help evaluate my assumptions? Would like to test switch...normally closed or open. Can I assume if healthy,a 12v signal should be sent to SLCM? Help Mr Wizard. Thanks all

 

The electrical diagrams for the X308 are part of JTIS and also available as a separate .pdf linked in the stickies.

Without those aids, diagnosiis is a *lot* harder. JTIS will also have a set of pinpoint tests to guide you through diagnosis.

 

Not sure about the x308 brake light switch, but on my previous car I replaced one for about $8 - just unplugged the harness, snapped it out of the mount and stuck in another.

If the Jag is the same, just unplug the harness and stick a conductivity meter (the "ohm" setting on most voltage testers) in there and test if it opens/closes the circuit with the brake pedal movement

 

All,
Have changed out brake switch with new, but the prince of darkness for the brakelights still prevails. Have looked at schematics and felt certain that would heal the Jag. Open to any suggestions from the group as to how to proceed from here. Many thanks.