Graeme wrote:
I have a motor which runs on 16v AC. It has a double wound field
coil, and is more correctly a universal motor, as it will also run on
DC, but that is irrelevant, I think.

There are four terminals. Power runs from a transformer to A, which
is one side of the field coil.

From there, current runs through the field coil to B, and from B to C,
which is one brush. The other brush is D, from where current runs
back to the transformer.

To reverse the motor, wires are swapped, so that power coming out of
the field coil (B) goes to brush D (not C), and back to the
transformer via C, not D.

What I cannot work out is how to use a switch, or switches, to achieve
remote reversing of the motor. Ideally, I would have two push
buttons, one for each direction, but any switch would suffice. The
switch(es) need to be able to supply the power, and swap the way the
brush caps are connected.

Any thoughts on the switches I need, and how to wire them would be
appreciated. The motor only needs to run for about twenty seconds, in
either direction.

You need what's called a DPDT switch (Double Pole, Double Throw). You can
also get them with a centre-off position. If you Google for DPDT Switch I'm
sure you'll find what you need.
--
Dave Baker