Seasons Greetings Everyone:

I trust and hope you are all well !

However, you are probably all mad at me because I am the Grinch who stole - or bought - all of the Lamp Control Modules (LCM) for my (our) '97 XK8s on Ebay.

It seems that every time I replace the LCM, I burn out the R8 resistor in a matter of a few minutes to an hour. This results a a failure of the passenger (right) side running light(s).

Might anyone know for what the R8 resistor is responsible?

I have grounded both the light pods on both sides of the car.

As you can see from the photo, the center and far right / running and brake lamps are illuminated on the right side before failure. Just the running light on left.

Also, the lamp connectors on both sides have been replaced, and apparently the color coding for them is haphazard at best. I can trace the light path with an ohmeter, but I'm not really sure what's going where.

Also attached is a schematic I put together which is my educated guess for the arrangement of the tail lights. (I've seen some official diagrams, but even with the Google and my manuals, they are hard to (re) find.)

1) Is my light light schematic correct?

2) Any idea why R8 is frying?

3) Where might the short circuit lie ?

Thank you all !

 

First lets eliminate the ground wire issue, present in all our cars from factory.
they chose a wire too small to handle the current draw it can face..

Are you already aware of this issue? If yes, may I assume you've already corrected it?

If not, just say so and I'll write it up for you fast. unusual symptoms for this issue but without knowledge of R8 I'd be guessing.

Meantime I'll look at schematics for r8.
John

 

Reread. You installed separate ground wire both sides.
where exactly is r8? In LCM?

John

 

Website f'd up. Say more exactly what happens when you do what? Where is r8.

R8 blown open. Is it grounded? Measure each side 2 grnd.

sorry sounds curt, typed a lot, website goes white =

 

Google "jaguar xk8 lamp control module"

One result will be from this guy on this forum https://www.jaguarforums.com/forum/m...consult-22380/

From a 9/15/09 date. Lots and lots of good info / work around for this problem.

John

 

TG,
It looks like you have your tail and stop lamps reversed? From the '97/8 vehicle care:



R8 in the LCM is for the 5W RHS tail lamp. IF you have a 21W bulb in there, it will burn out. Replace with a 1.5 ohm 5W wirewound.

Although both side and brake appear to be lit on the RHS, so there may also be a short between the feeds to the cluster, or on the cluster itself?

 

Wow great catch Michael!!!

 

Thanks Michael for the information! And Johnken ! This is most helpful...

Ok...so both sides have the extra ground wires.

It is the R8 resistor that blows out in the lamp control module...That is, it is now an open circuit - no resistance...You can see the burn marks...I'll replace that resistor with one from another (fully destroyed_ burnt out module.

Now, with the diagram, I can now go to the right side light assembly and determine where the fault lies.

I'll make sure it's a 5w bulb. (That seems so simple, and yet I didn't think of it!) And as you suggested Michael, there is likely a short between the tail light and the stop light. Before you posted the diagram, I was only guessing on the locations of the lights. (The fog and tail light on the left side might be reversed as well, but I thought I had taken care of that...will revisit.)

I'll report back soon. My spirits are buoyed. This has been a long battle !

 

For MY 2001 onwards the bulb at Position C is a twin filament bulb - a 5W tail light and a 21W stop light - so there are four tail lights in total. The electrical diagrams also show the bulb failure sensing to be different for the two different arrangements. An incorrect MY bulb sensing unit will interfere with the wiring order to the cluster and could be your problem?
Edit this morning!
Further looking shows the plug arrangements for the two modules to be different so can't be interchanged. However, are your resistors all the correct values for your MY ?

 

I had a similar issue with my car (2003 XKR), not blowing the resistor, but not getting enough juice to the right side taillight. A new ground did not fix it, so I ended up (prepare to cringe) running a wire from the left to the right to get them all to work. I still got the tail light warning message, but at least everything illuminated. I saw nothing wrong with the fixture or any connections within it.

When I first bought the car, a bulb (B) was burned out. When I replaced it, both (B) and (C) would dim to nearly nothing. I swapped bulbs from side to side, no help, new ground, no help, and then my kludge.

My final solution, as always, was to sell the car.

 

Thank you Astromorg and BimmerGuy! My '97 has a dual filament bulb in position C. For some reason, the lamp modules are surrounded by caulk, though there is no apparent body damage around them (The previous owner's cure all for everything was to squirt caulk on it.) It's possible the lamp modules were replaced with later model modules. Who knows? I don't recall how I arrived at ordering LAMP-CONTROL LJA 2245 AD /05 8200 00 replacements to fry. When I bought the car, the previous owner had thrown away the LCM box and soldered together the yellow connector. It took me months to even realize a control box was missing (but I was trying to get the car running at that point!)

Still planning to report back soon...This week, if not in a day or two !

 

All the bulbs in the early cars should be single filament, and the corresponding location in the rear lamp cluster should have only one contact.

It is possible to retro-fit the later rear clusters, but they are not a direct fit and need some metalwork changes. As astromorg notes, the later clusters require dual filament bulbs in both the tail and stop positions, although the stop filament on the inner bulb isn't used.

The bulb fail sensing in the later cars was incorporated into the SLM rather than having a discrete module.

Here's the information from the later care guide showing the differences. Note the shuffling of the bulb position legends just to help things along:

 

Hello All,

As Michael suggested, it seems my rear tail lights have been replaced by later model assemblies as there are dual filaments under the outer lenses.

Unfortunately, it also seems that the lamp control module is not robust enough to handle the dual filament bulbs, along with the 21 watt tail lights.

Adding to my issue, my lamp control module is bodged (blob soldered) together, so it doesn't function quite correctly. With the ignition on, I always have running lights in the outboard positions. So, while I have a good idea on how to work around the problem, if I'm wrong, I'll burn up another LCM (which would be number 5 !).

Anyway, it seems the brake and tail light positions are swapped on the left side. This doesn't burn up anything, so my work around will be to do the same on the right side. Further, I'll also replace the 21 watt running light bulb with a 5 watt bulb.

At present, I've removed the bulb on the right side. My tail lights and brake lights now work under the same lens (and I may have destroyed the circuit board connection so that I don't get dual brake lights on the left side...but can't be sure until I get a new LCM).

So to summarize, I'm going to flip the stop and tail light wiring positions on both sides, replace the 21 watt running light bulbs with 5 watt bulbs. And cross my fingers that the latest LCM will hold up (to be ordered after testing with the bodged LCM) .

Not sure how universally helpful this post has been because it's probably rare to find later model tail light assemblies in your car. But you guys have helped me keep one XK8 on the road, so thank you very much! I appreciate you !

 

Mr. Graphics,

The main thing I didn't like about my Early XK8 was the Tail Lights. They were always messed-up...I was back and forth to the Jaguar Dealer....I never did understand them! All I can say here is "Good Luck!" and Thank Heaven Jaguar changed this on the later Cars!

Billy Clyde @ Cinco Ranch