I agree with Mark: If the bulb lights, it's NOT bad.

I have the '95 truck (& PF) service manual.  No relays.  Just a dirt simple circuit
where the flasher supplies an intermittent voltage, and the turn signal switch and
hazard switch distributes it to the appropriate bulbs.  All three bulbs (front, rear,
dash) on each side are in parallel, so if they behave differently, there's a wiring
problem.

Based on the orignal description of the problem, I think there's some damaged
wiring, probably in the front, that's shorted some of the headlight wiring to some of
the turn signal wiring..  Was truck in an accident?  The headlight circuit is quite
independet of the turn signal circuit. Since the turn signals work OK when the
headlights are off, turn signal switch, hazard switch, flasher, and fuses are OK.

And now that I think about it, the wiring damage is probably right around the
front headlights or turn signals.  Anything else would have made something else
not work.