If its a later model(88 up)it might be the printed curcuit board thats built into the rear tailight assembly,they rot out and cause all kinds of goofy problems. If it an older rig,it could be bad grounds,sockets,even the bulbs can have a filament break and touch the other filament and cause feedback problems.You cant really diagnose this kind of problem without being there,but theese are a few things to check out. /forums/images/graemlins/crazy.gif