Spark Coolant Temperature Override System
This system alternates distributor vacuum advance vacuum source between carburetor ported vacuum and manifold vacuum, depending upon coolant temperature. Two types of CTO switch are used: a single-function switch for models with standard cooling systems, and a single-function switch for heavy duty cooling systems. The CTO switch is threaded into the left rear of block on 6 cylinder engines, and into the thermostat housing on 4 and 8 cylinder engines. On some models, this system is used in conjunction with the NLVR valve.