I have a 1997 Burick Park Ave. Left turn signal is OK. Right turn signal is twice as fast. I know by past experience that a bulb must be burned out and sure enough a rear bulb was out. I bought a new one from the dealer and replaced it. Now all lights work but the right signal is still twice as fast as the left. What could be the problem?

Bad turn signal relay or you have one bulb out on that side grounding out.

Or the blinker relay is on the blink. Do what Rev said first, make sure you don't have a short/ground jump happening someplace and then if all fails, replace the blinker. I've run into this with replacement bulbs before... but that wasn't because of the bulb, it was because I replaced things with a LED module for which the resistance is all wrong. That blinker relay is set up to do that fast blink when the resistance is wrong.