I have a call into Dan, thanks.
But I don't think this is the usual resistor problem. In that case you put a resistor in parallel with the LED which
1) Provides a load that simulates a light bulb so the tow vehicle sees that.
2) Does not drop the voltage to the LED.
In this case the low "sensing" voltage is enough to barely power some of the LEDs (the sensing voltage would not illuminate an incandescent bulb).
I could put a resistor in serial with the LED...that would probably drop the sensing voltage low enough to not flicker the LED, but it would also drop the full voltage applied for braking/turning. I'd be concerned that might cause it to not work right when I actually need it.
So it looks like the brakes and turn signal use the same wire. I assume they both apply the full 12V
, and the difference between braking/turning is the flashing? Or does one use a different voltage? Anybody know?
Actually I guess I could just always tow with the running lights on; the problem only seems to happen when the trailer is plugged in and no lights are in use.