Start by checking your earths!

Start by checking and cleaning the earth point on the right (drivers side) of the transfer box, all the earths from the rear of the vehicle go to this point. Then clean up the earth point on the left (passenger side) of the transfer box, this is a thick cable between the transfer box and the chassis - at which point the battery earth cable is also fixed. If this does not clear the issue, work through the individual earth wires for each light, and also the heated rear screen.