I have a 1977 F-250, only the rear turn signals don't work. Hazards, brakes, running lights work fine and front turn signals work fine?

If your hazards work, that would tell me that the wiring from the turn signal switch or the signal switch itself is bad. Check your connections at the base of the steering column.

Thanks Mark, I pulled the wheel and put a test light on the switch, when switch is in on position the lead with the blue wire flashes, but no flash on the red wire. Should both wires show flash? is the blue for the front and red for the rear turn signals?

I found these wiring diagrams. Maybe they will be of some help:

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Thanks Mark, I've got those but dont really understand them. There are two leads that come from the turn signal switch, just wondering if both leads should show current when signal is on.

I studied the drawing and According to the diagram - Blue wire is your 12 vdc from the flasher (main 12v from the fuse block) Right rear is Green and left rear is Yellow/Black. There will be a constant 12v on the blue untill the switch is made. Once there is a load places on the circuit, the flasher will engage. You will have a alternating 12vdc to 0v on the green when the lever is down and the same on the Yellow/Black when the lever is up. An analog meter will be helpful here, a digital meter may not be fast enough to see the voltage with the flasher in the circuit. You could temporarily jump out the flasher with a piece of wire so you get a constant 12v on the blue wire. Hope that makes sense.