70-71 Auto TCS Transmission Switch

(GM Part 8683502)

Transmission Controlled Spark (TCS) System controls exhaust emissions by eliminating vacuum advance in the lower forward gears, while at operating temperature. The TCS intake manifold solenoid controls vacuum to the distributor's vacuum advance unit. The solenoid determines when, and how much, vacuum to release. Typically, a vacuum line from the carburetor enters the solenoid and another vacuum line exits the solenoid to the distributor vacuum advance unit (some applications have multiple inlet and outlet lines). The TCS solenoid relies on an electrical signal provided by other TCS system switches/senders via an electrical connection on the back or side of the solenoid (Engine Harness or TCS Harness plugs into this connection).