Number Plate Lights. Wiring

[DJPremier]

Evening all. Happy New Year :)

Asking here if anyone can help with diagnosing number plate lighting issues. The weeny lights are not working. Bulbs are good and the holders, though not great, are still conductive. The fuse is good. I'm sure its wiring break, or earth, but I'm not clear where to start with diagnosing where the fault/break is. I have a multimeter, So as a start I'm hoping someone can tell me.
1: where the number plate wiring goes from the tailgate into the body and where / if any connectors are in there that will help me test continuity.
2: Is it possible to test at the the fuse end by putting a meter between the connections in the fuse holder. To see if any juice is present across the fuse with the lights turned on. If no juice I'm *assuming* that means its the switch that's the problem ?
3: any other suggestions very welcome !

This is a dealbreaker for the MOT so I'm hoping to get it sorted this weekend, in between freezing my butt off outside. Don't have a garage or a driveway. After about 30 mins at 1degC my hands and brain stop working TIA !

[GT_II]

The first thing to check is that you have zero resistance between the lamp holders and earth. Reading from the wiring diagram for 1985 on Sciroccos (let me know if yours is earlier), the lamp bodies are connected via a brown cable to an earthing point on the right C pillar. However, I think that may be a printing error and suspect there is an earthing point on the tailgate itself. Either way, there should be zero resistance between the bulb holders and any earthing point or bare metal on the body.

Next, with side lights switched on, check that you get 12V between the number plate light power leads (grey/green in the diagram) and earth. If not check for 12V between earth and the grey/green wires at the 2-pin connector stated as at boot rear left. From there, the wire goes straight through to the lighting switch (again grey/green), so you should also get 12V between that switch terminal and earth.

[DJPremier]

Fantastic. Thanks GT_II :) My car is earlier, a Storm. A 1984 B reg but I suspect the number plate wiring won't have been been dramatically different. I'll find out at the weekend. Awesome help as always on the forum.

Dave V

[GT_II]

I've just realised I misread the wiring diagram. The grey/green wire doesn't go through to the lighting switch, but to a terminal on the fuse board, where there are several other grey/green wires, so if the fault is in that area, diagnosis could get trickier.

All appears to be the same on pre 85 mk2 injection models, except that the earthing point is described as cross panel rear. Again, I think this may be an error, as the diagram for pre 85 mk2 carb models says the earthing point is on the tailgate.

[james butler]

you can find the wiring in the boot on the passenger side behind the cover panels, if you unplug the connector you can test the earth and the live feed to that point.
this will confirm whether or not you've got power to that point. if you have power and a good earth then the problem must be between that point and your bulb holders.
its quite common for the wiring to fracture and break where it goes from the boot lid to the body of the car through the flexi trunking.
doing the above test will prove it.

[DJPremier]

Cracking James. Thanks for the extra insight. It was the routing of the wiring and location of the connectors that had me scratching head. I evidently need to go a little deeper behind scene. Take my inner boot liner out and look into the cavity. Found out that the boot light has stopped working too so hopefully get two birds with one stone.