Jerry,
As the contacts in the pump close, a one direction, DC current begins to flow
and the magnetic field that runs the pump begins to build. In a few hundreds
of a second, the pump completes one stroke and the contacts open. At this
moment, the magnetic field begins to collapse and a reverse current begins to
flow. The older way of dealing with this a capacitor wired across the contact
which will absorb the reverse current rather than fuel an damaging arc that
erodes the contacts. The new thinking, after a small diode that coulds stand
the current of the reverse flow, was to wire the diode (valve) backwards
across the contacts. It wouldn't pass curent around the contacts to build the
magnetic field, but it would quickly quench the reverse flow which is the
flow that damages the contacts.
If you don't want to re-invent the wheel, buy the original diode from Moss.
Make sure you get the right one for your year (the early cars were positive
ground). Make sure the year pump you rescued is the right polarity for your
car too. If you want to live a little more dangerously, get a diode from
Radio Shack. I know they have a 3 amp. See if they don't have one a bit
bigger to be safe or parallel a couple of them
Remember, wire it in the direction that it doesn't pass current to energize
the coil or the pump will just stroke once and not return.
R. Johnson - Dallas
'90 Maine Coon
'79 Midget
'76 Midget
'73 MGB
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