Definitely a voltage problem, or possibly a dirty ground somewhere. A flasher relies on the proper amount of current flow to make the bimetal circuit breaker inside it heat and cool at the proper speed. You either don't have the proper voltage applied to the flasher, or one or more of the bulbs has a dirty ground, preventing them from drawing the proper current. Do any of the turn signal bulbs burn dimmer than the others?
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!