The blinkers on my 89 Crown Vic don't work. When plugged in they light up the car like a Christmas Tree. It was missing a side marker but I replaced that and they still don't work proper.

The first thing to check is the bulbs AND the sockets. Check for frayed or broken wires. Next check the fuses. The turn signal relay should click when the turn signal or hazards are on. If not, replace it. The last thing would be the turn signal switch on the column. If the hazards work but the turn signals don't you could have a bad switch. I think they call it a multi function.mike

After reading all of your text it sounds like a ground short or the turn signal relay is stuck on

And where could he short be? If the signal is stuck on, do i need to replace it?

If you don't hear the clicking of the turn signal relay replace it. If that doesn't do it you could check on u-tube

Are the lights bright & get dim when brake is pressed? I had that on a Crown Vic & it was ground wire in trunk that metal rusted out around screw. Located behind carpet on driver side by taillight.