2011 4.4 TDV8

While at the tyre fitters today I noticed when they were moving the vehicle that the rear right brake light was not working. Passed MOT last week so assume it was working then.

When I got home plugged in GAPiiD (every home should have one!) and found - among other fault codes- Rear Right brake light failure - short to earth.

Cleared all faults and that one did not return but brake light still did not function.

Swapped light clusters left to right and fault stayed on right which seemed to rule out a faulty light unit.

I am fairly competent mechanically but never got beyond basic electrics.

However, found a diagram of the 5 pin plug which feeds the cluster (says it relates to late models but wire colours do not match) and got out my voltmeter.

Between No5 (earth) and 4 (taillight) zero volts. Switched on the lights 14.2 V.

Between No5 and No2 (stop lights) 7.4V whether brake pedal pressed or not.

Then checked No5 to 1,2 & 3 - all 7.4V.

Confused!!

As I result of the fault code saying short to earth I examined the loom which goes through a grommet and joins a larger loom at the rear of the boot area. It was very tight across the aperture where it goes throught the boot wall and there is no edge protection on the single skin steel panel.

I unwrapped the binding and could see no chafing or obvious damage to any of the wiring but lo and behold reconnected the lamp cluster and all works.

I have put some sleeving over the loom and pulled it through the grommet to give it some slack and will see what happens.

A couple of questions:-

Is this a regular fault? It does not appear to be from searching the forum.

What I am not doing correctly in my diagnosis?

Embossed in to the cluster is the voltage and wattage of the various elements and they are all 13.7V at different wattages so I had assumed I would 'see' 13-14V on the voltmeter when the different functions were switched on.

Any help gratefully received 2011 4.4 TDV8

2012 DV8 Westminster

Had the same issue last week on the N/S stop light not working. I can't explain why but I got as far as pulling the cluster from the body although not disconnecting it from the wiring feed. Unable to unplug it I think due to the cold temperatures. I was concerned about breaking the socket with the use of a screwdriver.

I sprayed it with WD40 for a another day attempt and wiped around the car body recess as a cleanup. Now all the other functions - rear light, indicators, fog etc. were working but not the brake stop light. Before actually bolting the cluster back though I tried the electrics again to find nothing worked now.
Thinking I had now made things worse I secured the unit with the two bolts and fearing confirmation I had made things worse.

All functions did in fact now work including the brake stop light. My guess is that the WD40 cleared the water present in the connections? Pleased Its back safe to use but perhaps that was the problem water ingress?

Time will tell but I had this N/S light cluster showing as a fault constantly on the diagnostics tool short although things were working. Cheers

Unfortunately the fault reappeared with no stop light on the n/side yesterday. Like Wiltshire’s130 issues no apparent cause we their wiring or the actual cluster unit failing. Any suggestions greatly appreciated.

Thanks