Cruse/Turn signal interaction.... I had that too. Turned out a light bulb (In my case.. Well I won't tell you because there are 7 candidates) was not properly seated in the socket,, Re-seated and all work
The seven candidates
Right FRONT, Left FRONT on the MH
Right Rear, Left Rear on the MH
Right and Left Rear on teh Towed
Towed GROUND lead, actually there are two of these, One on the Towed end, one on the MH end (only one on my case which is why I said 7) and yes.
I have had this problem twice.. The firs time it was one of the 1st 4 (I had no towed) the last time was right after I hooked up the towed for the 1st time (the last one). In all cases it was easy to fix.
I will add I did not expect the FRONT turn signal to be the issue. but on mine it was.. Just re-seated the lamp and it works to this day.
