Well... my test confirmed that this does not work - sigh.  Unfortunately
I didn't decide to build one for grins but since the one I had from U-Haul
didn't work.  I ended up with no right turn signals after installation, so
I double checked the trailer and car wiring and found it to be (at least)
as it was in the instructions.  I swapped the right and left turn signal
leads and no left signals!  Since the manufacturer of the thing just molded
plastic over all of the components, I've no way to see what might be broken.
  Anybody have any suggestions on where I might get one besides U-Haul?
VWRuss