As if this car and its quirks aren't enough lol.
I am in the midst of trying to make this new LED tail light arrangement work and I am hitting a couple of snags.
The two issues I have are dash bulb warnings and I am also dealing with a weird brightness issue. Both may even be related?
I never gave it much thought going into this project that there may be hurdles to jump over but it has been interesting to say the least.

Ok issue number one.
My new tail light design uses a series of halo rings that I bought and through machining and 3D printing, I built custom housings for them.
Originally, these halo rings had 240 ohm resistors built into them that dimmed the output but also made the lights "fade" off when shut down.
This wasn't going to work for my indicators and I decided to remove them all from circuit. This is what caused my SLM to burn up as mentioned in a previous post as the rings - without the resistors in place were pulling down 3 amps - each!
SO I couldn't go back to resistors and decided to go the PWM route instead. I found a good deal on a bunch of 12volt LED dimmer boxes, removed the PCB's from the cases and mounted them all to a common board. The original boxes had rotary knobs to set the dim level, so I opted to replace those with fixed resistors after I determined how bright I wanted the lights to be. So far - so good.
I had to redo all of the electrical wiring but that was easy for me as I work with that stuff all of the time.
Wired it all up and individually, everything was on-point. I then ran into my first of two snags. With the park lights on and one or the other indicators in play, the park lights go brighter when the indicator light is on. So - indicator on - park lights brighter, indicator off - park lights back to normal. This happens regardless of which side indicator I am running.
The second issue is with the bulb out warning system. I had LED bulbs in the old tail lights and I had used load resistors to prevent the indications. Worked fine for the brake lights and also for the indicators but I always had a bulb out warning on the parks even with the load resistors in play. It is still the same today with the entirely new arrangement.

So by all means, dive into the plethora of electrical love I have left here and hopefully I can get to a nicely functioning set of rear lights but what I would like to know first is what amount of load is the park light sensor looking for when in operation? I have tried 2 variations of the load resistor. The first being a 25watt 10ohm load and the second being a 50watt 6ohm load. Neither stops the warning on the display although either one works on the brake lights.
Pics for your amusement.

 

Do you know the wattage of the original bulbs? If they are 5W you would need a 30 ohm resistor. 10 ohm is the equivalent of 15 watts and 6 ohm the equivalent of 24 watts.

For your brightness problem, I would try wiring the PWM board for the park lights completely separately (in your photo it looks like your grounds are daisy chained) - maybe a voltage drop or some kind of interference is causing the issue.

 

I do not know but I have a few regular bulbs sitting around and can do some checking.
I thought the same thing on the series connection of the grounds. I did that to reduce the mess of wiring that would be needed.
First thing I tried was isolating the ground as you mentioned. Only hooked up the left indicator and the park lights with one ground going to chassis and the other going to the battery negative. Made no difference so I put that back the way it was.
Does not appear to be anything grounding related per se. I can clearly see all grounding to the setup so there is nothing suspect going on there.
Hoping that if I can get the load resistors sorted out first, it might reveal something with this subsequent issue.
Good call on the grounding though as it kinda feels like a grounding issue at first glance.

 

Thats odd.
The tail light are normally 5 watts, and the brake and turn lights are 21 watts
On my 2000 XKR I have connected 3 x 5 watt bulbs in parallel on each side for the tail lights and has no warnings on dash.
5w 12 volt = 29 ohm
3 x 5w 12 volt = 10 ohm
So a total ballast between 10 to 30 ohm on each side should be fine.
You could measure the total current on each side, it should be between 0,4 A (equals 5w) and 1,2 A (equals 15w)

NB! My is an 2000, there may be some differences to your 2003

 

The electrical guide shows each side is monitored separately, so the resistors need to be the equivalent of one bulb for each side - how much latitude there is I don't know.

Of course the module might just be faulty and is showing a bad bulb whatever is connected.

 

You won't see any warnings, but you may damage the SLM. It monitors for reduced or no current drawn by the bulbs. The fuses monitor overload.

 

That was my thought.
I figured that the load resistors I had at my disposal were more than enough to load down the circuit but alas - it isn't working.
I refrained from trying any more load on there as I am already on my second SLM. I wish I had something at my disposal to incrementally increase the load until the warning goes out but I do not possess such equipment.
The brake lights work fine with the load resistor attached so I am baffled.

 

That would be the worst case coincidence as the old SLM was doing the same thing with the old LED lights that were on the car? Same thing, no other lights had issues except for the park lights.
I had just gotten used to it over time and maybe I will have to settle here too but I figured, now is my chance to dig in and see if I can finally find the issue.
My car never came with the original tail lights so I do not have a means to back up either.

 

Are you sure you aren't missing another bulb somewhere that is also monitored? According to the wiring diagram for my 2001, the number plate lamps and the side marker lamps are also monitored.

This post has the wiring diagrams:-

https://www.jaguarforums.com/forum/xk8-xkr-x100-17/resistors-led-tail-light-conversion-220189/#post2098861


​​ If you still have your old SLM you could take it apart and double check which lighting circuits are monitored.
​​​​

 

^^ +1

Try pulling tail light trunk fuses 19 & 21 one at a time and see if the error goes away. #19 also feeds the number plate lamps, and #21 the side markers.

 

On my 2000 the number plate lights and sidelights are not monitored. Only tail and brake lights.

 

Aye,
Up to MY2001 the lamp module was separate. Sidemarkers & number plate lamps are fed through it, but not monitored.

 

Thanks for the ideas to try.
Going to have a go at a few things today to see if I can get this under control.

So, I find myself to be a bit of an old-parts-hoarder lol.
On most occasions, I keep stuff like that laying around indefinitely but this marked one occasion where I saw it as being burnt to a crisp and with nothing salvageable, pitched it.
Figures that it would be the time when someone suggested I looked at the old unit lol.

Standby for more updates on this.

 

Still working my way through these issues but I must say that they do look pretty awesome at night.