CTO Switch
The coolant temperature override (CTO) switch is located in the coolant passage at right rear of cylinder head on 4 cylinder engines, at the coolant passage of the intake manifold, or at right rear corner of intake manifold near EGR valve on V8 engines, or at left front side of cylinder block on 6 cylinder engines. The inner port of the switch is connected to the EGR spark port on the carburetor and the outer port is connected to the EGR valve, or TVS.
Switch opens at 100°F for 4 cylinder engines, or 115°F for 6 and 8 cylinder engines. Below these temperatures, no EGR is possible.