Defective Flasher Relay. Replace it.
I trired swapping with a friend's who has the same relay and I have the same problem..
A burnt out signal bulb, a faulty blinker relay, a faulty blinker switch, a loose connection or a broken wire are all things that can cause the turn signals not to operate properly.
Check the relay. Turn signals work off of a flasher. Replace the flasher they are usually cheap. If that does not fix it check the signal switch. That is the thing that you use to turn on the turn signals. That is usually the problem.
try replacing the flasher. there should be two, one for flashers and one for turn signals
Signals can be sent by flaghoist, signal lamp ("blinker"), flag semaphore, radiotelegraphy, and radiotelephony.
Black=Ground Purple=blinker Blue=light+brake
I had the same problem in my 1999 Mercury Cougar, I replaced the flasher located in the blinker assembly. It was very simple to do. Flasher cost about $10
be sure you are getting current on both sides of your turn signal switch when you turn on the blinker. This could be the problem.
Flasher and fuse
Generally, the tail "light" and the tail light "blinker" are two different bulbs. Check the blinker bulb first. If it is OK, then it is likely a fuse to a flasher unit.
The bulb is bad. Turn signals and flashers use different bulbs.
You probably have a bulb out. Remember, the rear has two blinker bulbs