I thought this might be of interest to those who tow.  I was ready to hook up
my trailer to my /whisper Mazda /end whisper using a U-Haul three-to-two wire
converter.  Well after all was wired on both the car and trailer, I had
problems with the right blinker.  I swapped the connections reversing the
blinkers and the problem migrated to the left.  With the help of my pal Greg, a
better electronics person than I, we came up with a schematic for a converter:

GND = GROUND
TL  = TAIL LIGHTS
LTS = LEFT TURN SIGNAL
ST  = STOP or BRAKE LIGHTS
RTS = RIGHT TURN SIGNAL

GND  ------------(white)--------------------------------------    GND
TL   ------------(brown)--------------------------------------     TL
                                       |\ |
                                       | \|
LTS  ------------(yellow)--------------+  +----+-------------- LTS/ST
                                       | /|   _|_
                                       |/ |   / \
                                             /   \
                                               |
ST   ------------(red)-------------------------+
                                             __|__
                                             \   /
                                       |\ |  _\ /_
                                       | \|    |
RTS  ------------(green)---------------+  +----+-------------- RTS/ST
                                       | /|
                                       |/ |

  We are going to try it out today.  I'll send an update...
VWRuss
Massaponax, Virginia, USA