Most frustrating electrical gremlin I cannot solve... any helpers?

Hi,

I have a annoying issue I cannot find anywhere on the forum or internet.

My issue is..

Indicators flashing very fast and rear bulbs not bright.
When braking camera comes up on screen annoying at night!
Hazards make the heater display pulse in sync with them -
Also flashes the truckman centre brake light at the same time.

I have checked the bulbs..all good and dry
I have pulled off the trailer control module to verify that wasn't at fault
I have opened the trailer plug which is all dry and disconnected it to verify also

There was an auxiliary relay which was seriously rotten positioned on the right hand side under the bonnet which I have replaced. I believe this to be the tow bar electrical control which I am not entirely sure as when I took it off the indicators still flashed dimly.

No one can shed any light.

Has anyone experienced this at all? I would be very happy to solve this myself..

Thanks for any help whatsoever...