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As I described in my post, testing your wiring is really easy, as is bypassing the switch, by way of a test.
Summary:
Drop the bulbs down, and check for 12V at the bulb. One end or the other will be 12V, because it is always present, if wiring intact, because it is the ground that is switched.
If 12V present, disassemble the latch area, and disconnect the switch itself. There is a coupler clipped to the back of the trunk lid. At the coupler, short the female pins together, using a very short piece of bent wire, which now replicates a 'closed' switch (boot open state). If the lights come on, the switch, or the short length of wiring to it, or the coupler is faulty. Most likely the switch.
Since the switch wiring is now out, test the switch side to make doubly sure, by using a multimeter, or power a bulb through it, if you don't have one. If it is confirmed faulty, struggle to remove it, and change.
By the way, £60 or so, for the switch from Jaguar, with a bit of wire and a plug. The micro switch inside, is made by Cherry, and I found very similar online, from Cherry, but the original model is obsolete now, so difficult to know if could be made to fit, but very much the same size and style. Guess how much. I was simply astonished.
Ok so I checked the Fuses, Checked the volts coming out of the Trunk plug (12 volts). Check the micro switch for continuity it's ok, When I push the Micro switch down when testing the needle on my tester goes on and off. I can put a wire across the bulb wires and they come on. glove box windows interior lights are ok. I'm trying to determine if the micro switch is the culprit. No codes, no warning light. New Battery at rest is putting out 12.3 volts.
Do remember what the Cherry replacement Micro switch parts number is? not the Jag number, the new cherry one. Trying to figure out the amps/ voltage for replacement.
I had the "stuck in valet mode" issue with my 1999 XJR. The button on the dash would not open the trunk (and the instrument panel lit up with, "Valet Mode.") The button on the trunk didn't work either. I was able to open the trunk with the key and see that I also had no trunk lights. I followed Sutty's trouble-shooting method. I first checked for obviously broken or damaged wires at the trunk hinge; all seemed good. I then checked the bulbs, which were good. Then I checked for 12V at the lights... nothing. Well, there were .02V, but certainly not 12. So, figured I had a wiring issue that was going to be a bear to track down. As a last resort, I decided to apply 12V to the trunk switch, wondering if that might trick the module into thinking the trunk had been opened. Voila! Everything went back to normal. Thinking about it too much makes my brain hurt... But I'm very glad I did not have to track down a wiring issue. I really appreciate all of the great ideas and information on this thread, and I hope my information helps someone.
I was having a BF trying to find out why the trunk lights, license plate lights, and the open button weren't working. Discovered it was broken wiring at the right trunk hinge as everyone mentioned. Even though all of the cabling looked fine; I opened the wiring loom and there were six separated wires and one on its last strand. I soldered them back together and all is working normally. It appears to be binding at the back of the hinge when closed so I didn't put the wiring back into the plastic cover on the hinge. I'm going to leave it out to give it more room to move.
So... the flexing caused those wires to break leaving the other wires in the sheath without damage.
That seems a little odd, and I would inspect the other wires for breaks you can't see.
Yep, they were broken inside the sheath. It looks fine on the outside but the wires are separated inside. It was a relief to finally get everything working again.
