Let me make a bit of clarification since I learned a bit about the problem since I started.

The problem is that the running light (the light that is always on with the engine) and the brake light (the light that is only supposed to turn on when the brakes are engaged) are both on, all of the time the car is running (or just on battery with engine off). When the car is completely off, the lights turn off normally.

Because both of these lights are actually two different filaments in the same bulb, I am not completely sure which is which, but that having been said I took measurements from the bulb electrodes. Left side, 12v and ~8v, and the right side 12v and ~11.8v

From other suggestions and Jim's advice I tried replacing all 3 solid state switches with parts I ordered from digi-key. The repair has had no apparent effect.

Ideally I could get my hands on a working LNG2600HB/008 SLM and swap and test, but these parts are incredibly rare and the only place on earth I was able to find one was Coventry West which charges $550 has a strict no-returns policy on all used parts. If I was confident it was actually going to fix the problem I would just bite the bullet and order one, but I don't want to gamble on that if I can avoid it. I'm close to just splicing my center brake light into my tail lights and just washing my hands of this problem...


My original post:

 

If the right side tail light stays on all the time, then you need to replace the Security Control Locking Module (SCLM).

If you have fine solder skill, it is possible to replace the defective chip on the circuit board, otherwise you can buy a good used SCLM part.

Here is a weblink to forum thread on this issue (see post# 84 in the thread, then view the other posts:

https://www.jaguarforums.com/forum/x...ed-bulb-10830/

Jim Lombardi

 

That's not the case, both lights do not turn on. The 3rd light does turn on. However considering the relay works fine I do strongly suspect the SCLM

 

Added Update 1:

 

I would say that if the tail lights are staying then you probably need to fix or replace the SLCM module.

I think our passenger tail light issued started that way then progressed to staying on after I turned the ignition off.

I had remove the tail light bulb to stop it from drawing power out of the battery.

Jim Lombardi

 

I replaced the 3 MOSFETs on the SLM board. no apparent effect, seems to have done nothing.

I *really* dont want to buy a 600 dollar used board on the gamble that it MIGHT work, especially if the repair I already did probably would have fixed it

 

Out of curiosity, I tried setting off the car alarm. The rear lights work correctly during the alarm (only one filament turns on).

 

Julio:
Please make a better description. You say "both lights do not turn on", which I assume means "Neither light turns on when I apply the brake". Right?

Then you say, "both are on all of the time but are unresponsive to the brake"! Do you mean you have voltage on the socket pins, when the bulbs are removed, whether or not the brake is pressed?


If I have all that translated right, then the first advice I would give is that there will be "leakage" in most electronic power circuits and if the load (the light bulbs in this case) is removed, you will still detect voltage with a high impedance meter. That is why a test lamp is may times better for testing circuits like lamps- the test lamp applies load. Or, measure the voltage with the bulbs plugged in.

If there is voltage, the lamps are good, and the circuit connections are right, then the lights will light. It is that simple.

Oh, if you really replaced the "high side solid state switches" with plain MOSFETS, the SCLM will not work correctly

 

Let me make a bit of clarification since I learned a bit about the problem since I started.

The problem is that the running light (the light that is always on with the engine) and the brake light (the light that is only supposed to turn on when the brakes are engaged) are both on, all of the time the car is running (or just on battery with engine off). When the car is completely off, the lights turn off normally.

Because both of these lights are actually two different filaments in the same bulb, I am not completely sure which is which, but that having been said I took measurements from the bulb electrodes. Left side, 12v and ~8v, and the right side 12v and ~11.8v

From other suggestions and Jim's advice I tried replacing all 3 solid state switches with parts I ordered from digi-key. The repair has had no apparent effect.

Ideally I could get my hands on a working LNG2600HB/008 SLM and swap and test, but these parts are incredibly rare and the only place on earth I was able to find one was Coventry West which charges $550 has a strict no-returns policy on all used parts. If I was confident it was actually going to fix the problem I would just bite the bullet and order one, but I don't want to gamble on that if I can avoid it. I'm close to just splicing my center brake light into my tail lights and just washing my hands of this problem...

 

OK, I am even more confused. AFAIK, there is no "running light" as you describe, only a light that comes on with the headlights. The brake light is the heavy looking filament, and the tail light is the lighter one. Are you saying, both filamants light brightly when the headlights are on and both go out when the headlights are off? Or is the smaller filament bright and the larger filament dimmly lit? If so, you have a ground problem on the socket.

If that is the

 

As of right now, both filaments turn on all of the time, regardless of brakes being depressed, and regardless of headlights being on. There is not a socket grounding issue, as these are the line voltages I am measuring directly out of the plug, with the socket assembly disconnected as well as from the socket posts. Interestingly, the voltages I am measuring for each socket electrodes are different (12 and 8 on the left, 12 and 11 on the right). However both filaments are on, again, all of the time. They do not, however, stay on when I turn the key completely off (key position 0).

Can someone verify wether or not the XJ8's tail lights are supposed to be on all of the time? I always thought they were on all of the time (not just with the headlights). Maybe my BPM has something wrong with it...

 

No, they are not supposed to be on all the time. The brake lamp is driven by the SCLM, and the Taillight is controlled by the BPM, so go figure. Unless you have suffered a massive case of bad luck, I think you will find the problem right at the sockey, but you are looking at it and I am not!

 

I replaced the BPM with one of the same SN and programming code. No luck, exact same symptoms. Tail lights on all the time, as well as brake lights (save for middle)

 

I suggest you do some careful step by step troubleshooting of the wiring harnesses from their source connectors to the sockets. Look carefully at the harnesses near the trunk hinges.