Karl, hazy recollection of this on earlier Fords.
Should be a block on the left fenderwell area with brake lines, 2 in (F &
R) and two out (ditto).
Little capped boss top center, with a wire sticking out. When the
differential gets upset, the sliding valve in the center of that block
moves to one end or the other, and turns on the light.
IIRC, you have to center that piston, leave a tool in there to hold
the piston centered. Bleed the lines, then then reinstall the sensor.
Light should be off then, good to go.

I have a 1996 F350, but it's not where I can look at it right now.
Besides, it has ABS. Not sure your 1993 does. But that may not make a
difference WRT to above procedure, as I think the ABS they used was a
downstream setup.

Thanks, I'll look for this.

I tried the bleeding the back brakes to balance. No joy. So i took it out on
the raod and hit the brakes hard. It stops great, but now I got an ABS
warning light too. There's a reason I quit trying to maintain automobiles
after the late 70s models.

I'm about to just take it in to the shop.

Karl