light problem

[chaunceyboyblu]

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