Got an '00 F-250 psd i turn on the RH turn signal and it lights ups correctly in the instrument panel and in the front and back (bulbs) , when i turn on the LH turn signal, it blinks rapidly in the instrument panel and rapidly in the front bulb (under the headlight) but wont blink at all at the back of the truck. Any ideas what is goin on here?

 

The blinker element in your LH bulb at the rear of your truck is burned out. It's kind of a warning to the driver that one of your turn signals isn't working on the outside of your truck since you can't see them when you're using them. If the bulb is okay back there, the turn signal switch may need to be replaced. They're about 40-60 bucks, not to hard to swap out. I did it in my wife's explorer, took about half an hour.

 

The relay can sense the decreased load when the bulb is burnt out and blinks fast to let you know that it is burnt out. If replacing the bulb does not resolve the issue, then I would think that it is more likely that the wiring between the rear bulb and the relay is bad than the switch.