Hi
Tip if you are having bulb failure warning light illuminate but all lights are working.
Maybe posted elsewhere but just had bulb failure warning lamp light up on the dash (54 plate touran SE), checked all round car, all bulbs appeared to be working. On removal of rear light clusters and removal of bulbs one at a time I found slightly corroded contacts which cleaned up with fine emery and replaced bulbs. Warning light has gone out.
Maybe worth a quick check and clean before digging deeper.
Cheers
Rob.