Hey All!
I've just purchased my fourth Jaguar and couldn't be more excited! The car is beautiful and it's actually very similar to my very first car (1985 Jaguar V12 Vanden Plas). I purchased it knowing the brake lights recently stopped working. I looked at the fuse and it was dead, so I replaced it, started up the car and pressed on the brakes and you could hear a crackle sound coming from under the steering wheel area followed by a very small stream of smoke. I turned the car off instantly. Also when I was applying the brakes, the lights would not light up. I could not track down where the smoke was coming from, but any ideas? A short somewhere? The switch? I tried starting the car up again and pressed on the brakes and once again there was a crackle and a small stream of smoke and this time the fuse died. Any help would be greatly appreciated.

1987 Jaguar XJ6 Sovereign

 

If you've had Lucas Smoke from under the dash, twice, and the fuse was blown when you got the car, then you know this has happened before, and by this time you should be able to see which wire has melted insulation; or at least it should show up as unusually shiny or drippy. Something is getting Really Hot and you should certainly be able to tell what it is by now.
(';')

 

Unless you are confident with a multimeter and reading a circuit diagram I would just take the car straight to an auto electrician or Jag shop if available. Thats a 35A fuse your blowing and wiring damage/fire isnt that far away.

If I was chasing this, I would probably do something like:

- hang a multimeter off the brake switch to confirm the short to earth (make sure the switch is mounted properly while your there)
- remove all brake light bulbs checking if the earth goes away
- remove the cruise control wire and check if the earth goes away
- if still there start working through the circuit systematically unplugging until I was able to isolate the location of the earth.

Others may be able to suggest a better method or know of a common failure.

This sort of thing is often related to work on the car and a poorly fitted part. See if you can identify any work around the tailights or loose wring at the cruise control (if fitted).

 

Holybananas:


I've a very strong clue. The fuse block in the drivers side (LHD) foot
well is fed from the ignition switch.


Then, there are two switches above the brake pedal. One is fed from the fuse block, the brake light switch. The other is cruise interrupt.


Access is tight and requires down and upside down work. Drop the
scuttle hatch to access. Two teeny screws at the top secure it. slotted.


You may have to open the A post cover to follow those wires.


Get Jaguar Schematic S57. I think it is available on this site for down load. Essential.


Learned of this last year, the hard way. I usually do it that way!!
A friendly motorist told me of "no brake lights". In my case, it was an ignition switch, "just plumb wore out".


But, it reinforced my understanding. Jaguar governs a lot of things via the ignition switch!!!


Side bar oddity??? I walked around my car, idling in he drive, in PARK, of course. Whoah, the backup lights a re on!!! Clearly seen in broad daylight!!! Normal, I have a vague recollection that tis is a side
issue of lumping. OK by me, no harm, no foul.


Congratulations and welcome. That is a very nice car!!!


Carl

 

Thank you everybody for your replies! I'm going to provide a little more detail. I've taken off a section of the underside of the dashboard to take a few photos. I found a purple wire that has been left disconnected, no idea what this is for or if it is causing any of this but thought I'd include it. There's also an area that I've circled in white that appears to have HOT damage. Hope these help.

 

what you are circling as hot damage just looks like rust to me, likely from an older master cylinder leak,or windshield. but dont take my word as gospel! others will chime in soon!! im with Carl though, get the s57, it goes a long way in helping you know whats connected to what and what colour wires are where!

 

When you said your wires looked like they were getting hot I expected something like this:

That white wire isn't stripped, it got so hot the insulation melted off and drooled down inside the harness, gluing the whole bundle together. (This jump wire is the band-aid the PO and his henchmen came up with. They didn't go quite far enough.) THIS is heat damage. If you're blowing a 35 amp fuse, you might look for something like this or a dead short somewhere in your brake circuit. You'll know it when you find it for sure.
(';')

 

Disconnect the cruise control release switch and see if anything changes. On your car somebody has already 'been there' and replaced the wiring connectors.

The cruise control release switch has an old-school-style cardboard partition that prevents the contacts from shorting out against the metal outer case. it's common for the cardboard to fall out of place...allowing a short. Often you can open up the switch and see actual scorch marks

Anyhow....

I can't remember if the stop lamp fuse is on a shared circuit with the release switch. But it only takes a second to unplug it and see if anything changes. Might be worth a try.

Cheers
DD

 

Alright so I am not sure if this is the brake light switch or the cruise control switch but while I was trying to disconnect the wires the entire black plastic connector came off of the metal housing and a few random bits fell out. It looks very burnt in it & a strong smell of burning (same smell I smelt when I applied the brakes and saw smoke in the past). I left it disconnected, popped a new fuse in, and applied the brakes. There was no burning smell, no smoke, the brake lights did still not work, but most importantly the fuse did not blow. I'm thinking this is the culprit right here. Is it possible the bulbs in all the brakes also blew because of this? Could somebody please let me know if this is the cruise control switch or brake light switch?

Thank you again everybody!

 

Oh yeah, THAT'S been hot!
I think you found the smoking gun, so to speak.
(';')

 

If its the switch with the red capacitor across it , its the brake light switch.

 

Thank you everybody! Now to try and find a replacement. Any suggestions where to find affordable parts? I've taken a look on eBay and I can't find a lot of them. I'm going to try a local wrecker.

 

Or, David Bodger @ Everyday XJ
He will probably have one and you don't have to remove it from the car!
(';')

 

Yup! I got mine there. They are fuyn to remove and replace!!!

Been there.

Similar switches side by side. Opposite functions. Cruise closed til pedal depressed, then opens. Cruise out.

Brake open til pedall depressed, closes, completres power to brake lamps.

Naah, I doubt that it blew two brake light bulbs.

Fuse did it's job.

Fix determined. At least half of the way home. Swap out the switch and all should be as it should.

Enjoy.

Carl

 

Update: Ordered the brake switch through SNG Barratt. Price was reasonable as was the shipping. It came with insurance & tracking and arrived much quicker than I had anticipated. I installed the part and voilą! Let there be light! Brake lights .