I had a similar issue and it was a blown fuse brake light. I was/am running 3-in-1 (Stop/run/turn) rears and have the installed the solid state gizmo to support the the LED signal.
Anytime Id activate the turn signal they'd go nuts, multiple blinking light front back and sideways.

Probably not your issue, but I'm bored and like to type =)

"stupid's in the water these days, they're gonna drink it anyways, until they don't know right from wrong..."