0333885 JOHNSON HOUSING, Bearing

The basics of the Engine Overspeed Indicator System are the same for all machines:* The Overspeed Indicator Control must be connected to battery voltage.* There will be two wires going to the control from machine ground. One of these wires provides machine ground for the control, the other ground wire provides machine harness code information. This allows the control to identify what machine it is installed on.* The control must receive an engine speed signal. This signal is generated from an engine speed pickup (sensor) mounted to the engine flywheel housing.* The control must receive an engine oil pressure signal. This signal is provided by an engine oil pressure switch connected directly to the control, or by the Ether Control on machines equipped with the MPPS Ether Control system.* When the control is receiving the proper input signals it will output a signal to activate the alarm indicators when the engine RPM exceeds a predetermined point.Components
D11N Components
(1) Test switch and warning lamp. (2) Engine overspeed control. (3) Engine oil pressure switch. (4) Engine speed pickup. (5) Ether injection control.
OHT Components
(1) Test switch and warning lamp. (2) Engine overspeed control. (3) Engine oil pressure switch. (4) Engine speed pickup. (5) Ether injection control. (6) Warning horn. There is no Test Switch on 768C, 769C, 771C, 772B, 773B, and 775B Off Highway Trucks.
994 Components
(1) Test switch and warning lamp. (2) Engine overspeed control. (4) Engine speed pickup. (5) Ether injection control.The Engine Overspeed Indicator system consists of engine overspeed control, engine speed pickup, test switch (if equipped), warning indicators and engine oil pressure switch or ether injection control.Engine Overspeed Control
Engine Overspeed Control
(1) Diagnostic Lamp #1. (2) Diagnostic Lamp #2. (3) Diagnostic Lamp #3. (4) Diagnostic Lamp #4. (5) Connector plug A. (6) Connector receptacle B.The signals the engine overspeed control processes are: Engine speed (RPM) - from the engine speed pickup.Test signal - from the test switch (if equipped) activated by the operator.Harness code signal - from the machine electrical wiring system.Engine oil pressure signal - from the engine oil pressure switch or from the ether injection control.The engine overspeed control activates the warning indicators when necessary.The engine overspeed control is equipped with four diagnostic lamps to provide assistance with system troubleshooting. The functions are:* Diagnostic Lamp #1 (1) - Green Lamp - When ON or FLASHING: indicates the presence of a engine speed signal (except during the power up sequence or a harness code fault).* Diagnostic Lamp #2 (2) - Green Lamp - When ON: indicates the warning indicators have been activated (except during the power up sequence or a harness code fault).* Diagnostic Lamp #3 (3) - Green Lamp - When ON: indicates the engine oil pressure signal is grounded (except during the power up sequence or a harness code fault).* Diagnostic Lamp #4 (4) - Red Lamp - When FLASHING rapidly for an extended period: indicates the control has diagnosed an internal problem (except during the power up sequence or a harness code fault). The control has failed. The machine wiring harness provides machine model information to the engine overspeed control. The machine harness code consists of four harness code wires which are either open or grounded. The combination of opens or grounds on the harness code wires, tells the engine overspeed control what the machine model is. Connector B (6) is a receptacle type connector and contains the four harness code wires.
Engine Overspeed Control - Front Of Cab (776B And 777B Shown)On the 768C, 769C, 771C, 772B, 773B, 775B, 776B and 777B, the engine overspeed control is mounted to the front of the cab, behind a panel to the right of the steering column.On the 785, 789 and 793, the engine overspeed control is mounted to the front of the cab, behind a panel to the left of the steering column.On the D11N, the engine overspeed control is mounted under the platform in the left foot area.On the 994, the engine overspeed control is mounted in the electrical controls compartment.Engine Speed Pickup
Engine Speed PickupThe engine speed pickup is a two wire magnetic pickup device mounted on the engine flywheel housing. The engine speed pickup provides engine speed information by signaling the engine overspeed control when a flywheel gear tooth passes by the engine speed pickup.The magnetic pickup is a single pole, permanent magnetic generator made of wire coils around a permanent magnet pole piece. As the teeth of the flywheel ring gear go through the magnetic lines of flux around the pickup, an AC voltage is generated. A positive voltage is generated when each tooth goes by the pole piece. Each time the space between the teeth goes by the pole piece, a negative voltage is generated. Engine speed is then determined by the frequency of these signals.On OHT's, the engine speed pickup also sends a signal to the tachometer.
Engine Speed Pickup - Top Of Flywheel Housing (785 shown)The engine speed pickup is located on the engine flywheel housing. Some machines have more than one pickup mounted to the engine flywheel housing. When servicing, check the harness wire No. to verify the correct pickup.OHT's - Wire No. 450-YL.D11N and 994 - Wire No. 788-YL.Test Switch
Test Switch - Dash (776B And 777B Shown)The test switch is a normally open, momentary-contact switch which connects to electrical system ground when depressed. It is used to allow the operator or mechanic to test the warning indicators and the related system wiring. The test switch (and warning lamp) located on the front dash. The 768C, 769C, 771C, 772B, 773B and 775B OHT's are not equipped with a test switch.Signal Source - Engine Oil Pressure
One of two components provide the engine oil pressure signal for the engine overspeed control. On machines equipped with a MPPS ether injection control, the ether