Bulb failure system and towbar
If you are referring to the 10 pin socket at the rear centre of the boot below the locking mechanism, there is a harness listed (Vauxhall part number) which connects to the 13 pin euro towing socket. I enquired at the local dealer but was told it was not available in the UK.
The bulb failure system is I beleive the "Check relay" feature, this can be determined by looking at the centre dash display, remove a side light bulb and check if you get an error message on the centre display.
If you are fitting a single electric socket then you can purchase a harness from Vauxhall which connects directly to the rear LH and RH light clusters through a plug and socket. This picks up the tail lights only, the fog lamp is on the boot and you have to cut this wiriing and reconnect through "crimp type" fittings to get the trailer fog light to work, all the necessary parts are in the kit including the heavy duty flasher relay, which has to be mounted in the boot. The kit automatically disconnects the rear fog lights on the car when you tow a trailer.
This harness also includes a socket for a trailer "Check" relay, which has to be purchased seperately, if you don't have the check function then the kit is provided with a dummy plug. If you fit the check relay you will need to pick up a positive feed to power this relay
Don't know if this helps?