Coolant Temperature Override Switch

Fig. 23 EGR CTO switches:

This switch, Fig. 23, is located on the left side of the engine block on 6-258 engines.
When coolant temperature is below the specified rating of the CTO switch, there is no vacuum signal to the EGR system. The switch opening temperature is 85° F for switch with white body, 115° F for switch with black body or paint dab and 160° F for switch with yellow body or paint dab.