CTO Switch

CTO switch is located at coolant passage of intake manifold (adjacent to oil filler tube) on V8 engines or at left front side of cylinder block on 6-cylinder engines. The outer port of switch is open and not used. Inner port is connected by a hose to EGR port at carburetor. Center port is connected to EGR valve. When coolant temperature is below 115°F, no vacuum signal is applied to EGR valve; therefore, no exhaust gas will flow through valve. When coolant temperature reaches 115°F, both the inner and center port of switch are open and a vacuum signal is applied to EGR valve.