Graeme explained :
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.

I can't think of a readily available push button that would do this as
a single switch solution, but what is known as an intermediate switch
would set the motor up to run forward or reverse, with a separate push
button to act as the run button. Intermediate switches are used in
domestic and commercial lighting circuits, to add extra switches to a
two way lighting circuit.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk