Hard to follow but I think there is a tail light 12v path that is crossed with the left turn 12v path. I cant tell if the trailer has anything to do with it in your description. It sounds like the trailer hookup work is simply the time you found out about the problem.
One place a tail light connection can cross with a blinker connection is at or in a bulb. If the bulb has two contacts on the bottom and two filaments in the bulb. Weird stuff happens when you add more wire to share voltage and glow bulbs like plugging in a trailer. for this it is a good idea to run the r's up in the bus to overcome minimal voltage issues. LED setups may not even glow on less than 12 volts delivered.
One other often screwed up place is at the bus end trailer plug. you might want to untape the wires an have a look
If it is a issue that only arises when you hook up the trailer, I would try one other trailer to see if it repeats and learn if it is the bus or the trailer.
If all else fails take it to a equipment rental yard for repair
Greg of Tim&Greg
94ptca
--- In
WanderlodgeForum@ yahoogroups. com, "chaunceyboyblu"
wrote:
>
> Helo, We are trying to hook up a trailer and are having trouble with the lights. Without the trailer hooked up the left turn signals work only when the headlights are off. When the headlights are on the left signals on the bus do not work. All the other lights work on the bus. Checked voltage at the bus trailer connector and when headlights are on there is also 12v at the left turn signal terminal. Any ideas where to go from here? Thanks so much!
>
> Robert Rahn
> Kalispell MT
> 1988 pt40
>