(ET) Befuddled! PTO dash switch

["Max Hall" <maxo iname com>]

Hi team. We are bracing for a good whumpin' up here in the nor'east, so I
went out to check on the ET (a 15 with a snowthrower; see also
http://www.maxmatic.com/electrak.htm ) and found the PTO was not working. I
opened the dash up (from both sides) and cleaned out all kinds of detritus,
including an old mouse house!) and finally tracked it down, I think, to the
switch.

There's beffudlement, though: the PTO switch seems to be a vanilla DPST, 
but
I can only make the PTO contactors close if I connect *all three* of the
wires (each of which had its own spade lug on the back of the DPST switch)
together! What's the role of the third wire? Safety circuit?

Thanks to anyone who can shed some light... the snow... it's... it's...
(WHUMP!)

- Max Hall
- www.maxmatic.com
- Share the road.