You have two options for wiring a vehicle like your 1988 VW Cabriolet for diode style tow bar wiring. You can wire up the tow vehicle so that the taillights function like a combined system (2 wire), which in this case you would want a 4 diode kit. Or you can wire up your vehicle like a separate system where you would use a 6 diode kit.
For a 4 diode kit you would want the # RM-154 or for a 6 diode kit you would want the # 154-792-118158.
I attached an FAQ on wiring up the vehicle in either... view full answer...