on my 82 f100, the front tank would always read empty.  mechanic said it was
bad float.

it turned out to be bad/corroded connection at the tank.
I have a 88 F-150, 4.9L with dual tanks. About 2 years ago, the rear tanks
would read full, but once below 3/4, it would dance from empty to full. Then
about 1/2 tank, it fell to empty. No biggie. Just filled the front tank and
kept like 5 gallons in the rear as a spare.
Now the front has started doing the same thing. Is this a float problem or a
electrical problem. What is the fix for this??

   The floats are on their way to being "sunk" which is full or partially
filled with fuel.  It doesn't take much to do it, and there really isn't
much you can do about it other than replace the sender.

Sounds like faulty senders - no big deal to replace. They have been
doing their job for 17 years (or 15).