Reversing light/side lights come on together

[Chuck2]

When selecting reverse on mt TD5(1999) automatic the reversing lights and the side/parking lights come on together. This also happens when the main lights (headlights) are switched on. My wiring diagram does not make it clear how this happens. Any advice?

[alien]

Have you got a trailer plug fitted?
If so does it have a reverse light wire?
The reason I ask is often wires in the plugs short from water or damage.

The other thing to check is the tail lights are earthing properly.

[Chuck2]

Thank you for your input. I have checked the earth circuit and all is OK. There is a trailer plug. I have only just purchased the car and don't know how the wiring of the plug was done so will investigate this further.

[Chuck2]

Alien

You were on the money. The trailer connection from the wiring loom(not the plug) was full of mud. Once disconnected all was OK. Now only need to clean everything and test circuit. thanks again.