BOLT 3181726 - Caterpillar

2. Connect the GY wire, that was connected to the oil pressure switch, to vehicle ground.Disconnect the harness connector from the operator panel.Check for continuity between sockets 2 and 5. (Socket 2 is the ground for the operator panel; socket 5 goes to the oil pressure switch.) 3. Check for continuity between the ground connection on the oil pressure switch (B wire) and vehicle ground. 4. Turn the fuel OFF.Remove the oil pressure switch; put a thumb over the opening.Another service man must turn the main power key switch to the START position. (DO NOT TURN OVER THE ENGINE FOR MORE THAN 30 SECONDS).An increase in oil pressure must be felt. 5. Install a pressure gauge in the opening for the oil pressure switch. Make a test for oil pressure. Brake Air Pressure Indicator
The brake foot lever controls the air supply to each brake master cylinder. The pressure air sends oil to the front and rear disc brakes. If the air pressure for the system is low, the air pressure switch opens and causes the indicator to flash.1. Let engine run for several minutes to be sure there is enough air pressure.2. Check for air leaks, especially at drain valves on the air reservoir.Troubleshooting
1. Remove the Y/W wire from the brake pressure switch and put it to vehicle ground. 2. Check for continuity across the switch. 3. Make sure there is continuity from the pressure switch to vehicle ground.Then connect the Y/W wire to the switch again.Disconnect the harness connector from the operator panel. Check for continuity between sockets 2 and 8. (Socket 2 is the ground for the operator panel; socket 8 goes to the air pressure switch.) Brake Oil Pressure Indicator
This circuit has two normally open switches in series. There is one switch in each of the air-to-hydraulic brake cylinders. If the piston in either cylinder moves too far because of not enough brake oil, the piston pushes a rod which opens the switch. If either switch opens, the brake oil pressure indicator flashes.a. Check brake oil (fluid) level.b. Let engine run for several minutes to be sure there is enough air pressure.1. Remove the two GY/P wires from the 7V5647 Brake Oil Pressure Switch on the cylinder for the rear brakes (the cylinder that is more to the rear of the vehicle).Put both wires to vehicle ground. 2. Check for continuity across each of the 7V5647 Brake Oil Pressure Switches. 3. Check for continuity from the switch on the cylinder for the front brakes, to machine ground. 4. Connect the GY/P wires to the rear cylinder switch again.Make sure there is continuity from the switch to vehicle ground.Disconnect the harness connector from the operator panel.Check for continuity between sockets 2 and 12. (Socket 2 is the ground for the operator panel, socket 12 goes to the switches on the air-to-hydraulic brake cylinders.) Hydraulic Temperature, Engine Coolant Temperature, Or Transmission Oil Temperature Indicator
Follow the instructions given at the first of the section on the EMS operator