I had problems with my signals as well as a few other electrical problems such as lights not working sometimes and working fine other times. Like you said bumps sometimes helped. In my case I had two problems. My fuse panel was old and fatiqued. The only thing holding the fuses in most of the spots was gravity. I replaced them with the parts from a fuse block I picked up a Canadian Tire. Cost about $5.00 and almost everything was fixed except the signals. They worked sometimes and sometimes not. I replaced the electronic flasher unit and everything is good now.