Thank you for making me smile this afternoon.

I once had an old (1977) Buick Station Wagon with the fake wood on the side that was my snow car/lumber runs to Lowe's, which cost me all of $750 back in '90 or so. It was from NY, so a tad bit rusty. The brake lights on that one didn't always work either. I recall my first winter with the car, when I had a small skating rink in the footwell due to a leak. Rather than chase down and repair the leak, I drilled a hole in the floor to drain the water. Remember, I spent $750 to buy this car, all-in. One adjusts their tolerance for crap, depending on how much the crap costs.

That said, on my older BMWs it seems that most electrical problems are caused by a poor ground. Since the OP mentioned running a ground from the battery to the relay, I can't help but think that that's a big flashing neon sign indicating a bad ground. Somewhere.

 

I had an issue with grounding in the boot. In my car, next to the battery are three posts spot welded to the body. One of those post welds failed. I replaced the post with a stainless nut-sert.
Checking those grounds my be worth a look.

 

Same thing here. Grounding to the bulb holders... on both sides. Did the same fix as you, except ran the ground directly to the battery's negative post.

 

Let the nasty comments come forth! THE BRAKE LIGHTS NOW WORK! No need to rip the dash apart. No need to seek a replacement or a repair for a BCM or a TCM or BLM...BLM? Huh??

Anyways...simple fix that I will share seeing I started this.

1.) Remove park solenoid
2.) Insert a tiny screw in shifter housing after drilling a small hole in base to keep lock out pawl from re-engaging
3.) Cut micro switch wires to cruise control from brake pedal harness
4.) Scotch Lock two extension wires to new SLS 503 brake light switch OUTER two wires.
5.) Ground one wire to ground post on A pillar with A pillar cover removed
6.) Cut blue/slate wire on white connector under A panel kick panel cover
7.) Skin and twist two ends together and melt solder on them
8.) Wrap the other wire from brake light switch and solder to the other two

Voila! Brake lights work. No problems with any other systems. No warning light, no dash lights, no bells, chimes or whistles going off. It is so nice to step on the brake and see the reflection of the third light in the rear glass.

So, there is my fix. LET THE Nasty comments begin!

 

I only hope you print out the details of this fix and stick it somewhere the next owner can find it; because its not the fix I'd want to pass on to anyone else.

 

It sounds like the next owner might be Sanford & Son.

 

LOL That's the best quote of the day. Good one.

 

There's an ECM rebuild service on Ebay.
The guy has good reviews. I'm still learning systems to identify a similar related problem on my 97 XK8.
Thanks to the good guys here that spend a little time to help us. Yes, I see that Jaguar owners are refined.
I''m working hard to get there now. Best of Luck to You.

 

That narrows it down to either somewhere along the ignition-switched ground side of the brake switch; i.e. the white/orange wire (according to JTIS) or the blue/slate between the splice and the brake switch.

If you have kept continuity through EM1 (sounds as if you have) then the ECM will 'see' the brake switch operating, which will help keep the electronics happy.

Only issue I see is that the brake lights will still work with the ignition off.

 

1.) The only place this car will be passed on to is the salvage yard, this I can assure you.
2.) This car has had more hands on it than the Wailing Wall, trying to identify who did what, when and why would result in analysis paralysis .
3.) Heard mixed reviews about ECM rebuilding outcomes.
4.) My fix cost less than $5.00
5.) The car passed state inspection after "Sanford and Sons" repair.
6.) Yes, brake lights work while car off but battery shut off is used every time car is off so no brake lights while car is off.

Some, very few, of you "purist" guys kill me. The 97 XK has a reputation that precedes me. I'm glad you weren't working in mission control during Apollo 13 and would never appreciate women like Vesta Stoudt.

I posted this thread for all the others owners who have this problem and just want to get their XK out of park and drive without being rear ended. I post it so guys like the fellow in Florida won't have to spend 750.00 at a Jaguar dealership after doing everything I did, or was told to do by well intentioned knowledgeable forum members,

I will conclude by saying that the car is fun to drive, has nice power, good brakes and handles well. The owner is happy he can drive his car again without sinking a ton of money into it. Isn't that really all that counts??

 

Peter, As a fellow that has worked on Triumph's and MG's since the '60's, I can completely understand what you did and why.
We have a saying on the Forum's when we are trying to not only find the issue at hand but what did the PO (previous owner) do to find a solution that worked for a period of time or until he/she could get rid of it.
Some were amazing, some never made it to the new owners home.
With the understanding it's going to the knackers yard (English for junk yard), I for one, a Well Done.
A battery cut off switch, that will surely fix a unknown draw on the battery no one can find. That hardly ever happens to a XK, yeah right. LOL

 

Glad he and you are happy with the solution, and it suited your immediate needs. In the end that's all that matters since it's his car and your effort.

For 'posterity' (i.e. anyone reading this later), it might help to note that most of our notional timeframes here while trying to assist with your issue are indefinite. That is, every bit of advice given was trying to help you keep the car moving safely as long as feasible after you asked for opinions, rather than fix something that might be a temporary or counterproductive band-aid. Perfectly okay if you don't take the advice either, it's just advice offered freely.

On the other hand, as an Aerospace Engineer, the Apollo engineers and duct tape reference made me laugh quite a bit.

I'm not sure the allusion you were after is life-critical modifications involving thousands of man-hours of advanced expert engineeering tradeoff analyses and assessments to modify a vehicle (the lunar module) that burned up in the atmosphere a couple of days later.

In any case, as my son would say, 'good on you' and happy motoring to your friend.

 

Dale and all those that tried to help Peter on his journey.
Did he ever run a ground from the bulb and socket holder in the rear to a ground?
As a ground seems to be the missing link, I just don't remember that being part of the solution and we all, well, most of us have added that ground wire to both housing in the rear over the years.
Don't know how many miles will be added to this cars life but hope he will keep up with things like changing oil and suspension parts.
I've had owners that wanted to replace one spark plug on a MG, when they left, I didn't say "You'll come back, yea hear".

 

He noted that he checked resistances between various points (i.e. "... Have tested and tried all the usual routes...fuses, relays, brake switch, light module, continuity tests, etc. Nothing is working...."), so maybe between bulb housing and ground.

Would have been interesting to try this suggestion based on the upshot of the fix chosen (rewired ground at the front, cut out cruise, appears to have left the ECM and rear wiring in the circuit).

On the 'single plug job', when they returned, did they want to replace one more, or go whole hog and do two?

 

Interesting...

 

Or MacGyver.

Have a similar problem but will likely look for a more traditional solution. I have instructed my family that I want to be cremated, just not in the XJ8.

 

This one will beard to believe, but I had the problem yeas ago and could not find it, so took it to the dealer. They found the problem in the drivers seat module! I suggest looking there.