What's going on at the rear end?

Can anyone help me with this please? Stop lights, number plate lights and reverse lights not working on Mk1 Caddy - must be something common to them all right?
Fuses all checked.
Earth connections inside rear light clusters both checked and cleaned.
All bulbs ok.

Any ideas where I start?



I'm not a mechanic and don't know how to use a volt meter.

Earths Checked, but have you tested them from the bulb socket to ground (frame)?  Do you have 12V on the Positive side to ground, as you are missing something here.

The only thing that they all have in common is the Ground.  All the running  lamps work off the headlight switch.
The Stop Lights work off the Brake switch, and the reverse operate off the reverse switch on the Transmission.



All of them have separate fuses, so you either have no voltage from separate paths or no ground.

Check the plug on the fusebox.

Thank you. Where is the plug to the fusebox?

I know where the bank of fuses is, and if you lie upside down, you can see some large square plugs above that - relays possibly?

There is a white plug hanging there- not sure if it's always been the same or has come off something somehow, but I can't see anywhere it goes. The wire looks yellow and grey…?

Briano1234 said

Earths Checked, but have you tested them from the bulb socket to ground (frame)?  Do you have 12V on the Positive side to ground, as you are missing something here.

The only thing that they all have in common is the Ground.  All the running  lamps work off the headlight switch.
The Stop Lights work off the Brake switch, and the reverse operate off the reverse switch on the Transmission.



All of them have separate fuses, so you either have no voltage from separate paths or no ground.

 Thank you. How do I test the bulb to ground? Are there any other earth to check/clean? Where are all the switches you mention, maybe something is unplugged ?