WIRE LACING 0751578 - Caterpillar

How Low Oil Pressure Warning Works
Low oil pressure is indicated by the low oil pressure light AND the fault alarm, except where there is a short in a harness (as discussed in the following).
The 6T1546 Oil Pressure Switch is the heart of this circuit. When oil pressure is low [below 70 20 kPa (10 3 psi)], this switch grounds the 405-GY wire. When grounded, this wire connects the BK wire of the 7T9157 Fault Alarm to ground through its steering diode in the 9R2400 Diode Harness.
When the engine is running, and oil pressure is above 90 kPa (13 psi), the 6T1546 Switch grounds the 400-GN wire leaving the circuit open for the 405-GY wire. Grounding the 400-GN wire turns on the service meter. This service meter has a "four leaf clover" wheel in the center of the dial face that indexes a noticeable distance every one second. Movement of this wheel means the 6T1546 Switch contacts have changed position to power the service meter after the engine is started. Earlier machines may use the former service meter which does not have a "four leaf clover" wheel.
How High Coolant Temperature Warning Works
High coolant temperature turns on the coolant temperature light and the fault alarm when the 6T2665 Temperature Switch closes to ground the 406-PU wire through its steering diode.
An Easy Check of the Low Oil Pressure and Hour Meter Circuit
To make a quick check of the pressure switch, notice if the low oil pressure warning light and fault alarm are on while the key start switch is "on" and the engine is off. This is a correct condition and means the "normally closed" contacts of the switch are closed. The hour meter wheel should not be turning. Start the engine. The low oil warning should cease and the service meter wheel should begin to index. This means the 6T1546 Switch has now changed to close the "normally open" contacts and is working correctly.
Analyzing Harness Shorts
If a low oil pressure warning is indicated while the engine is running and the service meter is turning, look for a harness short-to-ground (frame). If only the fault alarm is on, look for a short-to-ground between the BK wire at the alarm and the steering diode in the 9R2400 Diode Harness (under the dash, behind the steering column). If the alarm and light are on, look for a harness short in the 405-GY wire between the diode and the 6T1546 Switch. The 6T1546 Switch cannot ground the hour meter and the warning horn at the same time.
This same method is valid for troubleshooting the coolant temperature circuit.The most likely location for such a fault is at a Sure-Seal® connector clip. For a low oil pressure warning with the engine running, check the forward most connector under the operator's seat. (Be sure the engine has correct oil pressure with service tool gauges.) A clip that is either too small or damaged could cut through rubber the connector housing and ground the 405-GY wire.