Technical brake light issue

[sprie]

I replaced a faulty reversing camera. The power to the wireless camera was tied to the side lights.
During the installation i noticed that
a) the brake lights come on when the side lights are turned on
b) and when the side lights are not turned on, when the brake pedal is pressed, both the brake lights and the side lights come on.
Both sides.

I obviously need to fix this.

Any suggestions of which end of the van to start the investigation (could it be tail light cluster or is it somewhere near the brake pedal)?

 

[ZaphodB]

I replaced a faulty reversing camera. The power to the wireless camera was tied to the side lights.
During the installation i noticed that
a) the brake lights come on when the side lights are turned on
b) and when the side lights are not turned on, when the brake pedal is pressed, both the brake lights and the side lights come on.
Both sides.

I obviously need to fix this.

Any suggestions of which end of the van to start the investigation (could it be tail light cluster or is it somewhere near the brake pedal)?

Bad earth at one or both of the light fittings.

 

[sprie]

Bad earth at one or both of the light fittings.

Think you are right.

Cleaned up both clusters but no change.
Disconnected all the wires from nearside cluster: when i turned on sidelights, the brake lights on offside cluster did NOT come on.
The nearside cluster is very corroded (plastic bits come off in my hand when i move it) so I think that cluster may be the issue.
I will get a replacement, hopefully (fingers crossed) that sorts out the issue.
thanks