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.

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  • Have you checked the size of the earth wire on the trailer side of the plug - sounds like it is small - can depend on the quality of the cable... Cheap ones are all the same size (14/010), better quality used to have a 28/030 cable for the earth... – Solar Mike May 22 '19 at 15:38
  • @SolarMike I haven't checked the size of the earth of the trailer. I've connected the trailer to another vehicle and it works with no problems at all – JackU May 22 '19 at 15:51
  • checked for loose /poor connections on the pins? – Solar Mike May 22 '19 at 16:04
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    It could just be that your electrical system can't provide enough power for all those lights to run at once. I have seen that on many other vehicles, though I have no specific experience with your model. – Moshe Katz May 22 '19 at 22:01

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