TUBE AS 6N4551 - Caterpillar

Illustration 3. Location of cap, knob and rod.--------------- END SUPPLEMENT ---------------Description of Change: One of two new latching fuel solenoid assemblies is used in the above models. One of the solenoids is for 24 volt systems and the other is for 12 volts systems. The new solenoids have a different internal design, intended to eliminate internal corrosion and failure.Adaptable To: The new 9X5512 Latching Solenoid Assembly is a direct replacement for the former 12-volt latching solenoid assembly. The new 9X5524 Latching Solenoid Assembly (24 volts) is a direct replacement for the former 7T7744 Latching Solenoid Assembly. The two former solenoids are canceled. Description Of Operation (Both Former And New Solenoids)
These solenoids use an internal mechanical latching mechanism to hold the solenoid in the "run" position during engine operation. There are two coils in the solenoid. The "START" coil is energizes during engine cranking, and pulls the plunger into the solenoid where it is mechanically latched. The "STOP" coil disengages the latch and allows the plunger to move back to the "fuel off" position. The solenoid contains a switch that disconnects the "STOP" coil when the solenoid is in the "fuel off" position. During engine operation, neither coil is energized. Illustration 1 shows a typical wiring diagram.
Illustration 1. Typical wiring diagram.Illustration 2 shows the wiring connections on the end of the solenoid. It is important to connect the wires correctly. The "GND" terminal has a M5 threads, and the "START" and "STOP" terminals have a M4 threads. If the wires are reversed between the "START" and "STOP" terminals, the engine will not start and the "START" coil will be energized when the key switch is turned off. This causes the fuse to blow.
Illustration 2. End view of solenoid. In a typical circuit, voltage is present at the "STOP" terminal when the key switch is in the "off" position. There is, however, no current flowing in the circuit after the solenoid has returned to the "fuel off" position, because the internal switch has opened.Manual Override Feature
These solenoids can be operated manually if necessary. Remove plastic cap (1) and pull on knob (2) to put the solenoid in the "run" position, where it will latch. Push on the knob to unlatch the solenoid and allow it to return to the "fuel off" position. Keep the plastic cap on the solenoid during operation and storage to prevent contamination of the internal mechanism.
Illustration 3. Location of cap and knob.