Tony Drews' explaination and diagram links are correct. I have the six
terminal
switch from Pegusus (which continues to work fine after 6 years).
The key is that in addition to the main pair of high current switch contacts
for the
battery, there are TWO other pairs of lower current contacts. One pair is
normally
OPEN and one pair is normally CLOSED. When the switch is in the ON position
the
high current contacts are closed (making contact) and so are the set used to
supply
the ignition power. The other set (at this time) are OPEN and doing nothing.
This set
is used to ground out (through a resistor) the power circuit on the
alternator side of
the switch, WHEN THE SWITCH IS TURNED OFF.
So the switch, when turned off, not only breaks the battery supply to
everything but
also disconnects the ignition from the alternator (which is what turns the
engine
off) AND ALSO keeps the still spinning alternator from seeing a sudden NO
LOAD
condition which is what (I guess) potentially damages it.
I must confess that the arguments for the heavy battery connections being
cut off on
the ground side rather than the hot side make a lot of sense. I didn't
think it through
at the time and my cutoff switch continues to be wired on the hot side.
Kelvin Palmer
VSCDA, MC
MGB#34 Blue
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