The turn signal flasher relay is defective, replace it.
Flasher is under the dash, drivers side, follow the clicking sound the signal makes when turned on. That sound comes from the flasher. If signal is staying on it could be you have a bulb or two out. Check your signal lights before replacing the flasher.
You know a turn signal has burnt out when the light on the dash flashes very slowly, or just stays on until you cancel the signal. I don't think there is any way to know that it is about to burn out.
Sounds like you have a short in your wiring harness for your rear lights. As for your dash turn signal light, your dummy light is just acting up. You probably need a new wiring harness for your rear lights.
Typically if the turn signal lamp on the dashboard stays on (i.e. does not blink), it means you have a burned out turn signal bulb on either the front or rear of the car. This is especially true if it happens only on one side (i.e. left or right turn signal). If the problem exists on both sides of the vehicle, check your flasher unit.
I've seen some turn signal dash indicators that stay on without flashing just when a bulb is burnt out. If the signal itself is flashing, and especially if the turn signal arm doesn't automatically retract when you turn, there may be a broken spring in the canceling cam inside the steering column.
One of your bulbs is burned out. Replace it and test. To determine which one turn on your signal and see if one bulb stays lit with the other not doing anything. Otherwise, check them both and replace the one with a bad filament.
If a signal light stays on, but does not flash on a 1989 Pontiac, there could be a light burned out in the turn signals on the exterior of the vehicle. It is also possible that the flasher unit has gone bad. The flasher unit is under the dash on the driver's side.
Defective turn signal switch.
Get a new blinker unit.
In some vehicles, a consistently lit turn signal indicator dash light acts as an error message. What the light could be saying is that either the bulb is burnt out and needs replacing, or there is an error with the related fuse.
try replacing the blinker under the dash that little box that makes the blinker sound
Bad flasher unit or turn signal switch