Sidelights and heated rear screen

Recently I've noticed that most times I put my sidelights on, the indicator on the heated rear screen switch illuminates sometimes straight away, sometimes after 20-30 seconds. When it's in this mood, turning the heated rear screen on also illuminates the sidelights! Am guessing it's a short or bad earth somewhere, but everything behind the switches looks fine. Anyone had this before? I think I might have to look at the loom where the cables go from the body to the tailgate - any other ideas? (1995 993 hijet van)

Hi take off the indicator and head light with the trim on the drivers side there is a load of wiring there I had to repair our central locking wiring and had to go in there to get to the broken wires.

That's a useful tip, thanks.