Howdy, Jaguar Enthusiasts! I’m back with another gremlin...

2006 S-Type 4.2L V8

The weirdest thing is going on with the center “High-Mounted Stop Lamp” HMSL or otherwise known as the “Center High-Mounted Stop Lamp” CHMSL.

The symptom is that the HMSL doesn’t work. All of the other tail lights work without any issues. I’ve checked them all: blinkers, brakes, rear fog, hazards, night running brake lights. No dim lights. They all work as they should with the exception of the HMSL.

To get to the HSML you have to lay down the back seats and remove 3 panel fasteners, and 3 bolts holding down the car seat anchors. You’ll take off the left and right seat belt ratchet covers, and the two rear cushion backs using the same white clip design as you’ll use to pull up the bench to access the fuel and transfer pumps. It took about 5 minutes to get to the HMSL connector that powers the led light. I tested the LED light by connecting a 12v power source. They work perfectly. Not issues with the actual HSML led light.

Now on to the connector for the HSML, it’s located just behind the seat cushions that drop down on the passenger side of the car towards the shoulder height of the passenger while in the car. The connector is a white 3 pin connector coming from the car yet only two of the pins are being used to connect to the led light bar on the HMSL. When I connect a test light to the + and the - pins I get an illuminated up bulb, however, when I let off of the brake the light doesn’t go off, instead it dims slowly, THEN - when I hit the brake petal again the light fails to light up at all. I found that to be kind of weird, so I did the same test with the actual HSML light. I could disconnect the light connector, hit the brake light, and then plug the connector and the HSML would illuminate 1 time, and then when letting off of the brake, the HSML would slowly dim out until it was off. If I hit the brake again, the HSML would not illuminate again until I unplugged it and then plugged the connector back together while the foot is on the brake. I was able to repeat this with the test light. It’s weird as heck!

Thus far I’ve tested the HSML led light bar. That appears to be good using a separate 12v source.
I then changed fuses F44, F53, F57 all 10 amps.
I had a spare brake petal switch and tested that too.

Since then I’ve confirmed that I’m having the same symptoms.

My next move is to evaluate all of the light bulbs to make sure that they’re properly spec’d.
Does anyone know if there is a relay that drives these lights?

Does anyone else have any ideas on how to diagnose?

Thanks for the help!

 

While I’m trying to figure out why this HMSL isn’t working as it should. Can anyone give me any pointers on how to interpret what’s going on in this schematic? Specifically the green area.

Thanks!

 

I had a similar problem with my car. After putting in the wrong tail light bulb, the right tail lights and upper brake light were acting like they were haunted. I replaced the bulb I put in that was wrong and they still were haunted (not doing what they were supposed to). I pulled all the fuses related to the tail lights, upper brake light is tied to right rear tail light, left them out for fifteen minutes or so and then put the fuses back in. It seems that the tail lights have their own little computer and pulling the fuses and leaving them out for a while before putting them back resets it. Afterwards all the lights including the upper brake light worked normal and their brightness was even too.

 

Quick update

I've confirmed that all of the bulbs are in spec. I've been able to confirm that the LED strip works with 12v.

I did try hooking the led strip directly to the brake lights and the HMSL works, but it pulses...

I came across this other post here:

https://www.jaguarforums.com/forum/x...orking-144436/

I found the post searching for "third brake light" and "Third stop light"

The symptoms that I'm experiencing are very similar to what CJ is experiencing, but I can't find any mention of a suppressor in the manual.

This is just bananas trying track these little things down. Any help would be great! Thank you!

 

Sorry I missed this when first posted. That ground wire (BRD to B to CA116) appears to be part of a shield. Now why is this line shielded? I'm not sure if it's protecting the light circuit from from external interference. Or is it the other way around, protecting adjacent circuits from this one? I'm thinking the former, simply because the reverse parking aid speaker is in the vicinity, and maybe pulses from that circuit could affect the stop light. Just a guess, so don't quote me on that.

Note the 10K ohm resistor, in parallel with the LEDs. Guessing again, but it's probably to help smooth out any pulsing. I wonder if that has failed. To check, connect your ohmmeter across both terminals of the light assembly and record the value. Now reverse your meter leads and try again. I think you should see a change of approximately 10k ohms depending on the polarity of the test leads.

 

One quick thought:

Do you mean you verified the bulbs are the correct part number? If that was all, I wonder if one of the bulbs is acting up. For example, a filament can break and then weld itself back together in a different spot, changing the amp draw. If it's a dual filament bulb, it can get really weird. One filament can touch the other and both still light up to some extent but not properly.

To summarize Proust: It may be worthwhile trying new bulbs.

 

@kr98664 - You’ve probably had another child and they’re about off to college. Things have gotten busy around here and I just haven’t had the chance to chase down this gremlin until now. I wouldn’t dare leave you all hanging. I’m sure the anticipation of solving this problem is just killing the forums.

Ok, on to some more diagnosis…

More recently, the car has developed a dim brake light on the passenger side (RH), and the reverse light not longer illuminates. I check continuity from CA10 to CA116 to make sure they’re all good. I’ll report more findings on that.

I removed the LED light assembly from the car. I’ve tested the assembly. It tests 9.99k ohms in both directions not matter the polarity. I’m not the most sophisticated electrical engineer, so I’m not sure if that’s good or bad. I think it’s good since it’s regulated through both sides?

I’ve got the whole rear loom unwound and if you look at the diagram above you’ll see “CAS84” which is the Y wire from CA63-17 to CA18-2 is that a splice? Should I be checking continuity from CA63-17 to CA18-2?

Also, the circle denoted as “68S” what does that mean? Does that mean that it’s part of the SCP network?

@Catmobile Thanks for the thoughts. Unless I’m mistaken, I don’t see how the HMSL is connected to the RH (Passenger). It sits on CA63-17 and it appears to be independent and controlled by the REM.

I hope to get this one solved. It’s super annoying and the last of the bunch for now. Fingers crossed.

 

I tested continuity on every wire. All grounds check out. I believe I have a bigger problem with the Rear Electronic Module. Something is wonky with the module. I see a bunch of rear control modules in eBay for less than $50, but I think I’m going to send mine into module masters for a rebuild. A bit more spendy, but it comes with a warranty.

https://modulemaster.com/products/ja...module-rebuild

Has anyone used the service to rebuild any of their modules?

I’m going to try it, and I’ll let you all know how it goes.

 

Thanks for the link and did you see that if you have brake light issues then the security module is involved? The link to the security module repair is dead and a search of the site does not show it either?
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All of the brake lights work as they should. It’s the CHMSL aka HMSL and the turn signals that are the problem.

I also clicked on that link and had seen that it’s not longer available. I’ll ask about it..