I've wired up a 13 pin trailer plug to my 1996 Defender 90. When I connect a trailer board and I put the headlights on (tail lights come on) and put the hazard lights on, the tail lights go dimmer when the hazards are flashing and then back to full brightness when they are not flashing.
I thought this was an earth fault so wired in another earth straight to the chassis from the 13 pin plug and I still have the same issue.
What is causing this to happen and how can I fix it?
Note: the tail lights on my vehicle also flash but it is not as noticeable as on the trailer. When the trailer board is not connect the tail lights on my vehicle do not flash at all.