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 bit.
also....from my experience, this could be as simple as a burned out bulb not allowing for a completed circuit !
On a 1996 Ford Bronco the turn signal flasher is plugged in to the fuse box
push in on the turn signal...
signal which remains constant over a certian interval of time.e.g dc voltage
its on the turn signal, push it in towards the steering column.
A hub can do that. Signal repeaters, for a general answer.
Check fuses and turn signal flasher
Best bet would be E-Bay
stay with the boat and signal for help.
It unscrews by turning counterclockwise. There is a small "flat" on the shaft to assist in removal.
i believe its signal, mirror, over the shoulder and then go
amplitude modulation is where we modulate our signal with a carrier signal amplitude changes but frequency remains constant in amplitude modulation