Wiring For Tow Bar

[Ben01438]

I'm an auto electrician by trade and have lost count how many sets of parking sensors I've fitted to Audi's but never touched or dealt with tow bars.
Now my bro in law carries bikes on the back with a very good rack but has been tempting fate far too long now & has asked me to wire in a number plate board with lights.
I recall some Audis I've worked on have looms ready for a tow bar harness to be plugged in. Is this the case on a 53 plate 2.0 FSI A3 (sorry that's all I know about the car off the top of my head) or would a bulb failure indicator problem occur if I wire straight into the back of the light clusters?

Thanks

[BarryRudd]

Im sure its way too late but for the archives
Audis before CAN BUS can be wired without any by pass relays as bulb fail monitors are passive.
After CANBUS you need to use a seven way by pass device (basicaly seven relays with intelligence to act on various voltages at the rear lamps) . You will find that suppliers of these devices recommend them for all modern cars but the rule for us electricians is the CANBUS one plus Italian, you can check the Witter tow bars site and if the wiring kit is £39 then you know that includes a 7 way device
Barry