Today thought I would mend the number plate lights. Both out. N/S now working. O/S still out. Measures 12v but when lamp connected 0v so suspect bad earth or broken wire in the boot/trunk lid.
I then noticed O/S side light was out. This is not included in the lamp failure warning circuit. I pulled fuse F18 RH engine bay and the rear side light didnt go out. I then realised that this is a very early car and the side light fuse is actually F5. The rear lights on these early cars are fused separately in the boot fuse box. So 4 fuses for the four corner lights!
This early car has a lamp control module on both sides similar to an XJ40 module but on a 40 I think the side light was actually the head light lamp fed with a lower voltage?
Anyway the side light doesn't work, no power to the lamp holder.
Any thoughts??
Photos attached showing relay layout near to washer bottle, early car with large brown multi plug and later XJ Sport with just a couple of relays in the same place.
I am now looking for a "Vehicle Care" book for this earlier car which has the correct fuse diagram.
The earlier cars also used a different electrical box for the towing a trailer situation prior to VIN 739427

 

Update I have changed the lamp control module for a known good one (from the other side of the car) and it still doesn't work. Next step examine the wiring diagrams which are not that easy to follow!

Does anyone know the part number for the "Vehicle Care" book for these early cars. The later one is JJM 10 16 12/60?

Thanks
Charles

 

I have now changed the body processor module & O/S side light still not working.
The O/S number plate light is still out and the wiring in the boot hinge area is ok
The quick fix is to feed both these lamps from the working N/S lamps but that may well cause confusion.
Next step is to check fault codes and wiring diagrams but still looking for those!
The strange thing is that the side light fuse F5 !also covers the wing repeater indicator light!
I have checked by pulling the fuse and it does!!!
Does snyone have any thoughts??

 

You need to study the wiring diagram for the side light. It's a fairly simple circuit.

If you have no power at the bulb fitting, then check the output at the lamp control unit. If you have B+ output there then there is a fault in the wiring from the control unit to the lamp.

If you have no output from the lamp control unit then check the B+ input to the lamp control unit for the sidelight and check the switching input (switched ground from the BPM). If these check out then the Lamp Control unit is faulty.

If not, go back to the BPM and check the output there (switching ground) and/or trace the B+ input to the lamp control unit depending on what fault you find.

 

Thanks for that. Do you mean the lamp control unit at the front or the one in the boot? I have changed the one in the boot for another s/h one from eBay. This unit immediately illuminated the previously dead number plate light but extinguished two of the four tail lights, one on each side. Side light still out! Conclusion is my rear module is faulty and so is the second hand one. I am waiting for another to arrive.....

 

I was referring to the Lamp Control unit at the front. The rear unit plays no role in the front side lights. I think the front light issue and the number plate issue are separate problems.

I've attached an annotated wiring diagram that shows the circuit you need to trace for the front RH side light which may help. Do you have a multimeter to test with?

 

Thanks for the annotated diagram, most helpfull. The BPM must be doing its job as 3 out of the 4 corner lights work. I will investigate further.....

 

Update! The switched ground RS30-2 (R2 on the 15 way black plug) on the RHS was not "switching to ground" I suspect a broken wire between R2 and the BPM. I have linked R2 RHS to R2 LHS as these join up somewhere anyway en route to the BPM and hey presto both sidelights now work!
Thanks to Brendan for pointing me in the right direction.
Now to tackle the rear light problem which I am 95% convinced is the rear lighting control module (early type with black & white plugs) I am still waiting for another s/h one to arrive as the two I have exhibit different faults as mentioned in an earlier post!

 

Good result, well done.

On the number plate lamp I suspect you are correct that the lamp control unit is at fault. If the number plate lamp is the only fault on the rear lights, it would be worth opening up the unit as it may be fixable.

The circuit diagram shows internally the rear side lights and the number plate lights are a single function (for one side). But they are output to different pins on the connector.

That suggests that there is an internal bridge for the three pins somewhere on the circuit board. You should be able to identify the pins and may be able to trace them back inside the unit. It may well be just a dry solder joint. Worth a look as nothing to lose.

 

I did take the lid off one of them and saw nothing untoward but will have another look. Each leg of the output seems to go through a resistor (why? lamp failure warning circuit? Although front side lights have the same resistor they do not seem to be part of the lamp failure circuit.) so maybe one has failed or as you say a dry joint. From the relay output on the board there seems to be a leg that goes to earth through an unidentified component, although it is drawn like the resistors. I do get 12v at the n/p light lamp holder but as soon as you apply a load the voltage drops to 0v. The second lamp control module I bought off EBay has the same tail light out on both sides so maybe the previous owner had fitted a lamp off too higher rating in these positions and blown the board. I have been using LED festoons in my n/p lights so that should have caused no problem.
It is possible however that during the fitting process the heat sink on the festoon shorted out the lamp holder causing the board problem. I did a post about this previously as the lamp holder tags have to be bent to ensure no contact with the heat sink. One of my other cars has been fitted with LEDs for about 12/18 months now with no problem and that is the daily driver (XJ Sport). On a car I broke the n/p lamp holder had melted probably due to higher wattage lamp having been fitted (warning)
I am pleased not to be not paying someone an hourly rate to find these faults!

 

Actually the front side lights are included in the failure circuitry. In your front side light issue above you would not have seen a failure warning as it is only displayed when the light is switched on - in your case the switching element was missing. Remove a bulb from the sidelight now and see if you get the warning.

Yes I think the resistors are for that failure monitoring. There shouldn't be a resistor on the number plate output as that is excluded from failure monitoring.

 

Hmmm.... interesting, Brendan, I could near SWEAR I've had the bulb-out WCA for a failed number plate light in former times. But I may be mistaken. My number plate lenses are a bit deformed from the heat and thus so loosey-goosey that I fear losing them and normally just run with them in a drawer with the bulbs sticking through the holes and retained by their spring clips. Sometimes they retreat into the bottlid and appear "out" when just "hiding" so I may be confused.


Interestingly, when I picked up the kid's '96 out in Phoenix, it had a side-marker out but no bulb-out WCA, even though it tests good at key-on. And when I obtained "Spruce Bruce" most WCAs on the IP were lit including the bulb-out.... curiously with no lights switched on. It had two side markers out and no bulbs at all in the number plate fixtures, which are free-floating in the boot. I replaced the side-markers and passed the state inspection, with no change in the bulb-out caution. When I last moved it into the shop for cam-cover removal, the bulb-out had assumed an intermittent or flickering posture (not a "real" Jag unless it sports a flickering light, eh?) with all lights switched off, and on steady with park lights switched on.

(Sorry, aviation terminology slips in from work and past-life fun, WCA=Warnings, Cautions, and Advisories" or "Wicca's" in casual conversation)

 

@aholbro1

Yes you're right. I just went and pulled the number plate bulb on mine and guess what... a bulb fail warning light. Just goes to show that I should check empirically rather than relying on Jaguar wiring diagrams. Thanks for pointing this out.

BTW in trying to put my bulb back in I managed to push the whole fitting in to the boot. So there's a little job for me tomorrow that I wasn't expecting to have the pleasure of.

 

Ha ha...not to worry, unless you have gorilla-arms, you can probably get a hand/arm between the bootlid and the trim panel from the side, just go in from the side that is adrift, fish around till you find it and stick it back through. Shouldn't have to dislodge any of the Christmas tree pins holding the trim on - I do it about once a month or so.

I was mistaken about Spruce Bruce, the bulb-less fixtures hanging from the inside of the bootlid are the boot interior lights. The number plate lights DO have bulbs....but I don't know whether or not they work, it doesn't have a battery fitted, just now. I've got the bootlid trim panel removed and the boot illumination lights hang from about the spot you'd expect the number plate lights to be, hence the confusion.

 

I just spent ages updating this and because I had been logged out all the text was lost.
So to repeat n/p light is included in lamp failure warning circuit. My RH n/p light is still out with no warning showing.
In the rear LCM Tracing 3 RB across the circuit board it goes to resistor R24 which appears over heated, the red band has discoloured. Shorting out the resistor the n/p light works. Eureka!
I could just short out the resistor but would prefer to replace as it may cause other problems. The X300 book helpfully quotes the resistor as 0.22 Ohms but it doesn't state the wattage. I assume as the lamp is 5W and the lamp draws current through the resistor then the resistor also needs to be 5W rated minimum. I can only find wire wound resistors of this rating. There are 6 resistors of this rating so assume 4 x tail lights & 2 x n/p lights. There are also 4 wire wound resistors on the board and I assume these are for a higher rated lamp, but there are 6 x 21W lamps at the rear??
Taking the s/h board bought off ebay two resistors showed the same discolouration. Shorting these out lit up the two tail lights that were not working. R23 controls the inner RHS tail light and R? below R18 controls the inner LHS tail light. See photo.
Does anyone know the part number for the Vehicle Care book for X300 pre vin 739427?
where it states the fuse description for the Right hand engine bay fuse box F5 = RH SIDE, DI, REPEATER, MARKER LAMPS
I have JJM 10 16 12/60 which is for a later car
There is also JJM 10 02 12/70 currently on Ebay quoted as a 1997 carX300 rear LCM < VIN739427

 

Good work to identify the faulty component. I don't know enough to be specific but I don't think your logic is correct in terms of the wattage you need for the resistor.

I think the wattage rating of the resistor does not equate to the wattage of the component at the end of the circuit. I think if you get a resistor that is the same resistance and the same physical size (or slightly bigger) than the original you will be fine.

Hopefully, someone with some electronics knowledge will be able to confirm.


The Vehicle Care book you need is JJM 10 16 12/50. I have it and could scan a few pages if you need me to.