Audi A4 trailer lights not working

[Condi]

My 2010 A4 has (I believe!) a factory fitted towbar, and for some reason I get nothing at the plug. Now, electrics arnt my strong point, so before I go and pay someone to find why, is there anything really obvious (fuse/relay/plug to the loom) which could have failed or fallen off? Nothing obvious as far as connections into the plug go, and I realise there could be 1001 reasons as to why, but to get NO electric at the plug suggests something simple, rather than a problem on one wire.

[rallycross]

it should also have a master fuse that leads to the plug, usually somewhere in the rear side panel of the boot (had the same thing with my 3 series a few months ago, was just a simple 15 amp fuse) - check in and around your boot left and right behind the trims

[Condi]

You're right, thanks. Its got a 16amp fuse which had gone.

And I did learn its not a factor fitted towbar, and someone has used scotch blocks to fit a bypass relay.

[HustleRussell]

Could've been a dealer fit rather than factory.