Ivan,
The thought occurs to me that the brakes in your '55 Overlander were
probably made to operate on 6 Volts. According to the Kelsey-Hayes
manual on the VAC web site, the 6 Volt magnets were about 2 Ohms
resistance and the 12 Volt magnets were about 4 Ohms. If you have two
axles, the resistance of four 2 Ohm brake magnets in parallel would be
only 0.5 Ohms, and the brake controller self-test routine might
interpret this as a short circuit. (Overlanders were made in both
single-axle and double-axle versions.)
The first thing I would do is check the brake current and operation with
a battery and an ammeter. (And a fuse in series, in case there is a
short somewhere!) If the brakes work, then they're not shorted. (At
least while you were testing them.)
If the brakes and wiring are actually OK but the brake controller thinks
they're shorted, one work-around might be to put a series resistor in
the line to bring the total resistance up to where the brake controller
expects it to be. (In those days Kelsey-Hayes sold resistors to operate
6 Volt brakes on 12 Volt systems.) Another solution might be to rewire
the brakes in series-parallel. If I were going to do that I think I
would wire brakes on opposite sides in series so an open magnet or
connection would still leave one working brake on each side.
Good luck,
John Sellers
1960 Pacer
WBCCI/VAC #1587