Finn Lassen wrote:

SPDT: Single pole, double throw. Means three connectors in addition to the 2 for the relay coil. Can get them at Radio Shack, if nowhere else.

            o--- B
A ---o
            o--- C

Draw an arrow from A to B, or from A to C.
A is either connected to B or to C, depending on power supplied to the relay coil or not.

Finn

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