I discovered my my front seat heaters were non functional after purchasing my XJ8, which traced back to the rear fuse box and one of the infamous "system relays".
Obviously it had been an issue for a while as the prior owner (or their auto sparky) had bypassed the troublesome relay as it also fed a supply to some of the rear light cluster functions.
So there were multiple additional wires added in the rear to cobble some functionality back to the rear lights as a minimum - no doubt to get the car through a warrant of fitness.

So as Pete said, have to remove fuse box, split the two PCBs apart to then replace the relays - I say relays as I suggest you just replace all of them to eliminate any future problems while you are in there!
You really don't want to be repeating the process by taking a short cut.
Note: You'll need a pretty powerful soldering iron as those heavy copper tracks disperse the heat efficiently, so a 25W iron just will not get the job done.
I ended up doing some careful preheating with a heat gun to assist my Weller iron.

 

Hello dear Fellows
As mentioned further up, I had those weird behaving rear lights. I was able to get a replacement Fusebox (used) and installed yesterday night. And I'm happy to say: The light-mare ended, the lights work perfectly now, also both reversing lights now work.
Was not able to check the driver's seat heater yet, to much snow for the XJ at the moment but will let you know.
I will have a closer look at the defective fusebox later - I don't know anything about the history of the used replacement part.
Regards from Switzerland, Beat

 

Hi. You guys seem like the right people to ask.

I'm looking to wire 2x rear side marker lamps into my x350 XJR. Where on the rear lamp cluster should I tap in to?

Thanks!

 

Hello Hunter
To be honest: Don't do that. What is your motivation to think about it? Actually, you would connect them in parallel to the rear lights - I can't tell you the connectors, never analysed. But think about the sophisticated electronics supervising the light cluster and also about the current drawn through the relays in the rear fuse box. Those relays are a weak point and I wouldn't stress them. If ever, use the lowest power consuming LED, you can find.
However - if you really want to do it - good luck .
Best, Beat

 

My 2005 XJ8-L already has side marker lights aft of the rear wheel arch. AFAIK your XJR is identical in that respect.

That said, both sides of those, (red) and both sides at front (amber) which are also turn signal repeaters, had corroded incandescent lamp sockets that needed replaced.

Whilst DEAD one might mistake them for mere passive reflectors? That seemed a good time to convert to LED's.

IF.. I had need of ADDING larger, brighter... differently placed.. wotever... lights to any of those?

I'd pick off their leads to operate a new and separate relay, fuse it according to the new load.

The complete electrical diagrams can be downloaded at no cost as a .pdf file.
Mind, IIRC there are over a thousand pages? Or mayhap that's the one for the Range Rover Sport?

Mark One human eyeball can find the wire to the existing sockets right quickly. MOST wiring has one or SEVERAL colour traces, and they have done a fair-decent - if b****y TEDIOUS - job of keeping them unique so as to make tracing easier than not.


2CW

 

Depends on what you want your marker lamps to emulate.
If you want them to provide turn signals then you would connect them to the wires I have indicated with Green circles.
However if you want the markers to simply be additional side lights (come on with the park and tail lights) then you will want to tap into the wires indicated with red circles.




To avoid any chance of overloading a circuit, if you use LED bulbs the additional current draw will be far less than using a conventional filament bulb.
Note: the LED bulbs are generally polarized, meaning they usually only work if the voltage is supplied to the correct pins. If you put positive to the incorrect pin then the LED light will probably not light ( so bench test the lamps to make sure you wire for the correct polarity).

If you are a bit unfamiliar with the wire colour abbreviations, then the first letter is the wire colour, the second letter is the stripe colour. Any wire with just one letter notation is a solid coloured wire.
O = Orange
R = Red
G = Green
B = Black
W = White
Y = Yellow
N = Brown
U= Blue

You will probably just intercept the appropriate wiring at the back of each 7 way connector of the respective tail light cluster.
The lamps in the clusters effectively have managed 12 volt supplies to them and the earth return is what is switched by the rear electronics module to activate the respective light functions.

Good luck.

 

Thank you very much for your help on this. I'm going to install these now.

I don't suppose you know where I could tap into for the front ones too?

 

Sorted.

 

Good work!
OK, same as before, the most likely semi-convenient place to pick up connection is at the rear of the headlights, unless you go further upstream into the harness.

Now....there is a bit of a GOTCHA here....see the colour codes for the wires for the turn and side lights for the left light assy...........they appear to reverse assignment for the right headlight plug.
Brown/White stripe is turn signal in left headlight cluster, but that colour wire is the side light on the right head light cluster.
The same goes for the Brown/Red stripe wire....which is the side light on the left and turn signal on the right.
(Don't ask me why an electrical engineer would do that to us, but they appear to have).
Both the turn and side lights are fed from the same B+ source, fuse F9 (10A) for the left cluster via the Orange/Yellow stripe wire and fuse F25 (10A) for the right cluster via the Orange solid wire - Passenger junction fuse box.

 

Perfect, thanks very much! Will get this sorted tomorrow and report back.

Very happy with the upgrade, it baffles me that we never get stuff like this in the UK. I think the only car I've seen over here with side marker lamps was the mk1 Volvo S40 about 20 years ago.

 

All done. Very pleased. Thanks to everyone who helped