Whats the side swicth for - General Electric GE 24-Hour Timer, 2-Pin #15004

15004 timer slide switch is to control timer mode.
When switch is one direction, lamp is ON all the time.
When switch is other direction, timer programs control lamp.

See 15004 timer instructions on following link:
http://waterheatertimer.org/GE-timers-and-manuals.html#15004

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