Hi Trev,
Whilst upgrading my 1997 +4 amber indicators to clear lens DRL/ indicator lights, it was necessary to swap light fittings and run extra cables some of which needed to pick up an earth.
I swapped the single bullet connectors for doubles as this was the easier way without the need to cut the existing wires.
My point is, that it was amazing how many of the existing earth connectors were only just holding into the connector and it was a wonder that I didn't have an earthing problem a long time ago.
So I would take the above mentioned path of checking the earths as a first point of attack. The earth connectors for the rear lights are easy to access if you look under the bumper and up towards the rear light cluster. I fount that removing the spare wheel helped with certain points of access.
Hope this helps..
Rob.
Last edited by BLUE+4; 26/05/20 02:23 PM. Reason: typo