My tow rig for the TTT is a 1998 BMW Z3. It is a small car but is great to travel with as long as there are no more than two persons. Good mileage too.
BMW sort of frowns on modifications and do-it-yourselfers. Because of that, finding an adapter to control the trailer lights was impossible not to mention finding an electronic flasher to carry the extra load.
To make the car and trailer compatable without these special items was not so difficult. I created a relay bank from used 12 volt normally open single throw relays. Junk cars are full of them. At first I was going to use relays only for the left and right turn signals but decided to incorporate relays into all the running light circuits which would not increase the load (measureable load) on any of the car circuits.
George (Ralph1931)
Create a bank of 4 or even 5 relays. Provide a good 12V positive supply to all the normally off ( the swinging ones) contacts protected by a 20 amp circuit breaker. Provide a ground to all of the relay coils. On the positive side of each coil, pigtail a signal wire from the tow vehicle harness. (a wire from stop (1), tail (2), left turn (3), right turn (4) and if you wish, from the back up lights (5)). Then from each stationary contact, connect a wire to the correct trailer harness plug. I added amber lamps to each side of the trailer for the turn signals.You could use red if preferred. This relay configuration does not work with combination stop and turn signal in the same filiment. Most later model vehicles do not use the combination signals anymore. My tear is wired this way and the little BMW doesn't even know it is operating those extra lights.