Do you know if you have DLR(day light running lights)?
If the head lights come on when E-brake is released or automatic trans is in gear then you do have DLR, only the head lights come on with DLR.
As Newman said, have you tried using the Multi-Function switch(turn signal stalk) to flash the brights, and does that work 100%
Fuse #14(15amp) in cab fuse box looks like it is the high beam fuse, with it removed high beams should be disabled.
For low beams each head lamp has a separate fuse, fuse #3 and #4 both 10amps.
These get power from main headlight switch but it does pass thru multi-function switch.
I would first see if it is the high or low beams that are coming on and then go from there to see what is triggering the on/off