Full size 1990 Ford Bronco and believe that the turn signal relay has gone out if that is the right term the turn signal remains solid but will not flash when engaged?
I'm not sure about a 1990 model, but later model fords have the
flasher unit incorporated within the hazard flasher switch. Try the
WD-40 fix, it might correct the problem. Spray WD-40 around the
switch and pop it up and down a few time and wiggle it around a
also....from my experience, this could be as simple as a burned
out bulb not allowing for a completed circuit !