1998 Renault Laguna short circuit in rear indicator

You have a bad earth. The indicator power is trying to find an earth thru the brake light wire.
Take the builds out and clean all contacts to bright metal, also clean the wiring plug, check ewarths with a tester and if any suspicion of bad or intermittent earth just scotchlock a new earth onto the indicator earth wire close to the bulb and run it to the car body, crimp a ring connector to the other end and use a self tapper to fix it to the body or fix it under another earth point already fitted, clean that up too.

could this fault be located on any part of the left hand indicator circuit?i recently removed the front of the car, including lights,to replace the radiator.

Possible I suppose but if power was tracking thru the front earths other things would be lit up when you indicate. IMHO

I'm sure its just the rear light issue. If its a circuit board type it may have got wet and white corrosion will let voltage escape to other circuits. Im sure if you clean up everything including the earth and or add a new one it will be ok

Thanks tony,will try swapping the rear bulb housings,if the problem switches to the right then its the bulb unit.

How did you get on mate?