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Home >> GMC >> 1975 >> Forward Control 7.4L Eng VIN Z, Automatic Trans, Trans Mfr CD 475/M40 >> Repair and Diagnosis >> Engine Performance >> Tune-Up >> Transmission Controlled Spark System >> Operation >> Time Relay Switch

Time Relay Switch

Relay is an electrically operated on/off type switch. When relay switch is energized through temperature switch, it opens normally closed relay points, opening circuit to vacuum advance solenoid. This energizes vacuum advance solenoid, and opens vacuum port providing vacuum to distributor vacuum advance unit.