In my quest to extinguish brake lights that insisted to remain on 24 hours a day and drain the battery, the brake light switches were replaced. Completely disconnecting the switch assembly beforehand didn’t shut them down so there was little expectation that would solve the problem of perpetual red lights. There’s been so much conjecture the brake lights were the root of all XKR/XK8 evils, it seemed prudent to perform the inexpensive transplant surgery, no matter how painful it had been described. All in all, it wasn’t as time consuming and horrible for me as previously described by some.

My recommendation is to first acquire a decent "headlamp" (not for the Jag but to wear on your forehead). The ability to visualize the components made it infinitely more serviceable than fumbling around in the dark.

My plan was to remove the switch assembly from the bracket as opposed to drop the bracket in its entirety. The driver’s seat was removed because the seat control module had been broken out and was frequently jammed between the seat and floor carpet. With the seat out, access wasn’t all that bad for my 6' frame. At first, squirming under the steering wheel wasn’t swift nor pleasant but after a few minutes, I got a smooth "plop, tuck and roll" in and out down to a science. Not bad considering my prosthethic knee had to be physically pulled in for the one leg to clear the rear window and my dislocated collarbone had to put up with the confines of a narrow footwell.

I swore the sound deadening material would not be torn to shreds, but alas, there is one small ligament of rubber that appears intended to be sacrificed when rummaging around under the dash, otherwise, it still looks at neat now as when service started.

A few moments of detective work revealed the intended target, the 8mm hex nut that holds the switches onto the bracket. A small wood stick was fabricated to hold the brake pedal down but the brake lever actually blocked access to the nut, so the pedal remained up. Using a 1/4” ratchet, 8mm socket along with an extension (my first choice was long extension that worked great but short extension may prove more appropriate), the nut spun off easily. The stud is fixed solid to the bracket so there’s no fumbling with a loose screw to hold. The top nut did not need to be loosened; it appeared there was a plastic spacer to let the slotted end of the assembly slide out and back in.

Now here is where I screwed up royally. The switch assembly lifted free off the stud but try as I may, the bracket wouldn’t come off. I rationalized the pedal drops down and the wire pushes into the cam so the switch housing must move to the front of the car. While that was true, it refused to come down. A bit of wriggling around focused the light on the tie wrap I’d forgotten all about!!! With a flip of my exacto knife, the tie wrap was severed and the housing pulled off without much ado. And yes, before I removed it from the car, the wire connection was unplugged.

The switch assembly looked good as new and the switches were clicking almost in perfect harmony. There’s been some discussion the switches must sequence with absolute perfect timing. I question that logic as the systems may be parallel but not interdependent on perfectly timed signals. If that were the case, any engineer worth his salt would’ve at least elected one double pole switch instead of two single pole switches. Even that would not have guaranteed microsecond timing. The Japanaese would’ve gone with maybe an optocoupler to actuate a couple of separate transistorized circuits. Nonetheless, the switches seemed to being doing their job with imperfect sequencing before and they’ll continue their imperfect existence.

Thanks to this forum, I scored a couple of D2HW-A211D‎ SWITCH SNAP ACT SPDT 100MA 125V from Digi-key for next to nothing. After a couple of dabs of solder, the switches were soldered in ready for service. Fit is almost perfect but the tips of the levers scraped the plastic cams so I bent them down a touch and smoothed the edges with a flapper wheel.

As for the brake lights that wouldn’t quit, the new switches didn’t resolve the issue, but that’s another story.

 

Be sure to check the built-in adjustment in the switch trigger. There is a built-in ratchet that allows for proper positioning of the trigger with respect to the cam off the pedal stem. If this adjustment is completely collapsed, the trigger may not contact the stem at rest and the ECU will think you are constantly on the brakes.

Separately, is your transmission shifting up through the gears as you accelerate off a dead stop? If so, the ECU knows you have your foot off the brake. In other words, if the ECU "thinks" you have your foot on the brakes, the trans will not shift up. Off the line, you would get stuck in 1st gear.

Normally, these lights are activated by a control module. If the car is powered off, pressing the brake pedal should not turn these lights on as the control module is off.

Next step is to check the 2003 electrical diagram on jagrepair.com and find fuses/relays involved in the circuit. If all of that ends up testing OK, it may be the control module in need of a rebuild/replacement, a very uncommon scenario. Can you tell if there was any type of wire hacking in the past? Maybe someone installed an extra amp in the trunk and needed a source of power, and somehow messed this up. As the lights are "always" on, it should be "easy" to track the problem down with basic tools like a meter. This car is EXTREMELY well documented, down to the wire colors and location of the harness connectors.

Best of luck, keep us posted.

 

fmertz,

Thanks for the response. It answers a few questions. The brake lights are just part of the laundry list of repairs on my latest acquisition. For example, the car constantly locks me in and only the passenger door handle unlocks the driver’s door. Windows drop each time the door handles pull, but they never return up, in spite of numerous resettings and hard resets. The FOB locks and sets the alarm, but does not unlock, open trunk nor flash headlights. The steering wheel moves in and out, up and down, all on it own. A newer battery has been swapped, kept topped up with the charger and it always runs well into the 14V range but full voltage didn’t resolve most problems.

The most annoying issue is the brake lights come on and stay lit when shut down, draining the battery. Starting out with only a valet key and locked trunk didn’t help the situation. The brake lights SEEM to behave properly when the key is in the ignition (at least parked in the driveway). However, the problem crops up as soon as the key is removed. The brake lights turn on and stay on (with the exception of a few occasions when it stayed off briefly or flashed a few times before staying on).

I’m VERY appreciative to this forum for providing a library of manuals, however, I can only find schematics on brake lights in 1997 and 2000 documents. 2003 literature omits the wiring diagram for those lights. The ‘97 & ‘00 diagrams show the Security and Locking Control Module regulates the rear fog lights, but not the brake lights. I removed every single fuse on the car and only the one fuse for the brake lights extinguished them. This was a strong indication some solid state device was powering the relay and not the brake light switches. Disconnecting the switches did not shut them down either. There is one manual that told me what I needed to know- the Driver’s Handbook: luggage compartment fuse box, Fuse No 8, 5 amps, “Right and left-hand stop lights via the security and locking module.” Unfortunately, that gives a hint that it is a solid state problem or a program glitch rather than user reparable hardware. I may have a way of working around this dilemma.

You mentioned the transmission will remain in low in spite of shifter in D. I’m so glad you pointed that out. The last time I drove it (one of only a handful of short drives) it failed to shift. Now that the brake light switches have been replaced, it shifts correctly (knock on wood).

In reading numerous accounts of replacing the brake light switch, the term “ratchet” had popped up suggesting the mechanism was more than just a simple cam. There’s virtually no information on the ratchet nor resetting it. I’d have expected to see that highlighted in the instructions if it was that significant. Interesting.

“Wire hacking.?” Well, it did come with a 7 wire trailer light harness with wires basically just stuck into various locations and it has a solid sate “converter” for combining turn signals with brake lights. I had hoped removing that bird nest would resolve the problem but no such luck.

 

Once upon a time I had an Audi turbo that had the brake lights on anytime the ignition was on. I did a whole lot of testing (brake switch, wiring, modules) to no avail, and just as I was about to throw money at the wall, I discovered I'd put a single pole bulb into a double pole socket. The single pole bridged both contacts so the taillights were able to energize the brake circuit. A stupid mistake with a zero cost repair.

 

I was one of the proponents of the switches having to have perfect sequence. Since both microswitches had tested good with my ohmmeter, according, I used a stethoscope and long nose pliers to accomplish that sequence. That method seemed to be the answer. However in a few weeks, to my surprise, the "Check rear lights" message returned. At that point, I'm thinking that since this switch assembly is mass produced, the microswitches are not "fine tuned". So, even though my switches "ohmed out" good, I bit the bullet and installed the same switches as you from Digi-key. I purposely "fine tuned" them out of sequence (brake lights on before cruise is cancelled while brake pedal is being depressed).That has been several months ago and I have not had any failure message since, despite trying to force an error by feathering the brake pedal.

 

Hmm, check Fig 09.3, Exterior Lighting, Rear. Seems to all be there.

Seems to all point to this security module. Might want to take a hard look at it. From memory, some of those have occasional shown some pretty spectacular self destruction with major burns on the circuit board, etc. Right there in the trunk, I believe.

 

When I got the dreaded message, the fault turned out to be a dry solder joint at one of the microswitch pins. Subsequent checking of them by watching their operation on AutoEnginuity clearly showed them not only working, but distinctly out of sync with each other without creating any problems

 

Section 9.3 shows F6 (5A) as the feed for the brake lamps, and F8 (5A) for the high-mounted stop lamp. I've attached the page from the 2003 electrical guide in case your documentation is missing it. This should help you to cross-check the wiring after removing the PO's spaghetti

Can you confirm whether it was F6 or F8 which you removed to kill the lamps? Does the high-mount remain lit?

If it was actually F6, then pull the stop lamp relay R5 in case something has been rigged to energise it on ignition shutoff.




Curious

 

No manuals gleaned from this website have Fig. 09.3 referencing rear lights; I have been working off the 1997 & 2000 schematics which effectively agree with the later schematic so kindly furnished. Thanks!

To sum up the problem, both fuses 6 & 8 are hot with the key removed!!! Fuse 6 cuts off L&R brakes lights. The middle stop light itself is defunct but fuse 8 would've knocked it out. By the way, whose bright idea was it to NOT identify or even number the fuses in all these fuse boxes? Jaguar? Lucas? Ford? Probably the same characters that located the valet switch where it is bumped when working under the dash, and yes, only a valet key was provided with my XKR. The Driver's Handbook gives the fuse number but no clue which is which. Even the cheapest cars on the market take the time to mold the fuse numbers and functions into the lid.

CLUES: Relay primary terminal #1 is always hot. There's no switch here. The relay coil will activate if terminal #2 is grounded.
Relay secondary terminal #3 is always hot. There's no switch here, either. The relay contacts are ready to energize the brake lights if terminal #2 is grounded
Brake switch is tied to an ignition switched ground to pull in the relay. Both the ignition switch and the brake switch must conduct to ground for the brake lights.
Disconnecting the brake switch wires/connector does not shut the brake lights off. One would have to think the brake and ignition switches are excluded.
Removing the relay turns them off. This would exclude EVERYTHING from secondary terminal #5 on, including SLCM, Lamp Control Module, wiring and lights.
This cannot be a simple short between brake switch and relay as it goes out with the key inserted. There is a solid state device powering the relay.
What's left? If you blow up the schematics, between the brake light switch and trunk fuses, in fine print "NOTE: BTS5 - Adaptive Damping Only."

I had noticed that in the older schematics and disconnected the Adaptive Damping Control Module but it did not shut the brake lights off. I'll have to dig deeper into that.

 

The fuses are numbered, but the numbers are so small I almost have to use a magnifying glass to read them.

 

Is it the correct relay and not defective? Have you tried swapping out a known correct/good relay into that socket?

 

Why, oh why? jagxk2003.pdf

Take a minute, locate the security module in the trunk, and open it up. See if there is any sort of disaster in there.

When working with relays, it helps to familiarize yourself with the standard layout of the pins so you can more intuitively work it, i.e. know where the pins to the power circuit and control circuit are (87, 30, etc.). Make a short shunt wire to power something without the need to activate the control circuit. Also, take a good look at the fuse boxes, there is more information on there than meets the eye. The standard relay pins are numbered (pull the relay off) and the fuses are definitely numbered, but in tiny print. Most of those relays are interchangeable, so you can take one known-good and move it around for testing.

Last, check the connectors in the schematics as they refer to ground/power points described in Fig 01. These have relays as well.

 

Swapping relays was one of the first checks performed. Relays give no indication of malfunction. Brake lights go out when key is inserted. They seem to work normal when the key is in the ignition and turned to position ll, at least standing still when I can check them. Having said that, the trip when the transmission failed to shift has me questioning them when driving around (hard to observe the brake lights while driving). I've since replaced the brake switches and the transmission was shifting fine afterwards. I'll have to have my wife follow to verify they do come on when braking.

And yes, I have examined the security, damping and lamp modules, and all look in pristine condition. I've been working on robots and robots systems since their early days and have experience handling boards and electronic devices. All grounds look as clean as when this XKR rolled off the assembly line. That was one of the big attractions for me seeing a Texas car in the ad with an engine compartment clean enough to eat off of, compared to the salt infested rust buckets I normally work on here in Michigan.

I appreciate the 2003 schematics, but see there's no mention of the Lamp Control Module, not that it matters. I did run across the brake switches circuits in the 2003 Service Training Guide under Engine Management Part 2. The ECM receives input from the Brake on/off and cancel switches, but has no control over the brake lights. None of the illustrations of this brake light circuit shows them tied to the Adaptive Damping Module; roaming through the drawings does illustrate the switch attached to the ADM but you have to put two and two together. Since that is tied in ahead of the relay coil, it is not impossible it is grounding/activating the relay when the key is pulled out. However, that device is fed directly from battery power, not switched on and off via ignition, so removing the key would not signal the ADM other than through serial communication. And the device input should not be capable of sucking in enough juice to trip the relay. Having removed the ADM should have extinguished the lights if it was the culprit, but I recall the lights remained on. More investigation later.

After considerable reading through this forum, I see the Security and Locking Control Module gets a bad rap, and maybe rightly so, but I'd like to consider it innocent until proven guilty. For one thing, just swapping it out would come with a price tag and secondly, I cannot find the last three digit suffix to the module... the device simply shows XXX and there is no VCAT tag to be found anywhere in the trunk. Literature does not tell me whether this device plays an active part in actually energizing the brake lights or a passive participation simply sensing the current from the relay for lamp out feedback to the display. I have to surmise it isn't just a signal to the SLCM, but the power through it via the relay and fuse as there's no fuse for the SLCM to blow in case of a short. I do see the SLCM has an output to the fog light relay coil so it is responsible for turning them on and off via serial instructions. The SLCM is powered off of the battery directly and not switched on/off, so the ignition switch does not activate and deactivate the device. The SLCM could turn on the brake lights due to a glitch from a serial signal (from what though, Body Control Module?) then it would do so even if the relay was removed, but popping out the relay shuts them off. Again, the fuses 6 & 8 go HOT as soon as the key is removed, and the feed to pin 1 stays hot even with relay & fuses pulled.... apparently, something is ground the primary, pulling in the contacts. If something like the SLCM or renegade trailer light harness was backfeeding the light circuit and fuses, pulling the relay wouldn't interrupt the power, but it does. More head scratching and detective work.

 

The lamp control module was integrated into the Security module for 2001 MY onwards. In both configurations, bulb integrity is checked by current sensing through low-value resistors (hence its susceptibility to damage from excessive current draw, and the related issues of dealing with 'bulb failure' messages when incandescent lamps are replaced with LEDs).

There is a note on splices in the electrical diagrams to the effect that not all the circuitry associated with a particular splice is shown, citing unnecessary circuit complication as the rationale. Unfortunately one outcome of this is that the whole picture isn't immediately apparent:- BTS5 being a prime example!

The feeds ('1' in a square box) route back to the High-Power protection module so are permanently at B+.

I can't immediately see* a way of deriving an 'ignition off' signal in the trunk, so perhaps follow the OG wire and disconnect back along its route: AC13-3, HH1-19 & BI1-9.

*There may be one but, like RJ, I sometimes need 'eye assistance'...

edit: Doh! you don't need to sense ignition off. NOT ignition on will work just as well.

 

"The lamp control module was integrated into the Security module for 2001 MY onwards." That's interesting, as this 2006 has what appears to be one in the pocket adjacent to the fuses. Disconnecting it makes no difference so I'll ignore it for the time being.

 

After more checking, it looks like everything in the corner of the trunk is blameless. With the brake switch, damper module, SLCM, lamp controller and fuse panel disconnected, the meter shows there is still some minor conductivity to ground, not a short circuit by any means, but the harness should be completely open.

Moving on towards the front revealed a bit of a meltdown. The connector is fused solid and will need some "plastic surgery." You'll notice bare wire showing, too. I wonder if this is why this Jag was traded in to a Buick dealer, then the dealer pawned it off to a used car dealer cheap.

. There's a wire pair that burned out (images 3 &4) that likely isn't critical, probably goes to the tone ring. You don't think that could have something to do with the code related to right rear wheel, do you?

we're getting warmer....

WE'RE HOT!!!

lousy photo showing one half of melted wire with connector on the right

the other half where it drops through grommet

 

Wouldn't you know, the wires that let the smoke out (throwback to Lucas electrics) in their meltdown were twisted pairs for noise reduction!

 

Let me wrap this thread up..........

When I acquired this 2006 XKR, the brake lights stayed on 24 hours a day with the battery hooked up and charged, but wouldn't you know it, it only came with a valet key and the trunk was locked. The battery had drained repeatedly probably for months while it was for sale and it needed jumping from under the hood to start every time. For a few days, I kept the charger on it and then found a way into the trunk.

The bottom line, there's nothing in the normal wiring that would light the brake lights without the key. I discovered, in the corner of the trunk, evidence that there was a really nasty short that melted quite a bit of wire insulation that let some wires short amongst themselves. Electrical tape indicates something shorted one of the two major positive cables to ground. Image 1 shows the location of the arc strike to ground, with a telltale bead left behind. Only one wire seemed to short out and that was to the backup alert which doesn't show any sign of life.

The wiring harness in back had to be cut open so wires could be separated and taped. Image 2

arc strike location


bird nest

The brake lights now shut off and behave normally.

 

Haha... Good show! I'm all over this!

Great detective work!

I have signs of a meltdown that leads into that major boot loom as well. Cause looks to be a super cooked convertible/hydrologic pump short that burned back and thru, into the loom. I wasn't going to go there just yet (planned to) but it seems I will need to... I'm soon to me struggling (after the holiday) with a really crappy battery drain problem on a flooded (H2O) 2003 xkr...

 

I was afraid my Jag might've drown in a flood, too, but Carfax said it hadn't, so I took my chances on it. I was dealing with a tiny trickle short in the wiring, pulling the tailight relay in, for a 4A constant drain, killing the battery, but had the advantage of bright brake lights helping me in my search. I pulled every single fuse on the car and they did not go out! Unplugging connectors in the trunk helped isolate my problem to the trunk but by then, the melted insulation was evident.

First, see if the little door on the ignition switch is closing, it energizes a lot of devices in preparation for switching the car on. Maybe a shot of WD40 will end that mystery. Everytime I inserted or removed the key, the little door shut off and turned on my brake lights, driving me nuts because there's nothing turning those lights on and off except the brake switch. Even disconnecting the brake switch didn't shut them off. Insane!

Afterwards, I might suggest starting with 12mm socket disconnecting the heavy positive leads on the fuse boxes one at a time to segregate large clumps of hardware quickly. From there, track down connectors and modules to disconnect. Good luck!