Over Crank Protection Thermostat Wiring

March 15, 2017

Building on the earlier blog post showing the common diagram for wiring a solenoid control relay often seen on the 39MT Delco starters, we have expanded to show the diagram using the optional over crank protection thermostat (OCP). This is the small two pin black plastic plug on the comm end of the starter.

The purpose of the OCP is to open when it gets too warm - usually caused by the operator cranking the engine for too long. The two pins are soldered to each other inside the rear housing of the starter - when it gets too warm the solder will melt causing the pins to no longer be connected and the solenoid control relay will lost its ground connection disengaging the starter. Once the starter cooled, the solder would become solid again allowing the ground connection of the solenoid control relay and the starter would operate.


Leave a comment

Also in Tech

Voltage Set Points

September 07, 2017

The voltage set point is the the voltage an alternator will charge at while running. This is set by the regulator in most cases, but....

Continue Reading

7940-7100: 16-19mm (3/4) Wide Belt Conversion Pulley

June 27, 2017

Some agricultural, industrial, and marine applications run a particularly wide V belt. When replacing original generators or alternators....

Continue Reading

Massey Ferguson TO-20, TO-30 12V Starter Upgrade

April 28, 2017

On the older Massey Ferguson TO-20 and TO-30 tractors, it is common to see the original 6V system upgraded to a 12V system....

Continue Reading