4-68 4203781 First Edition
ELECTRICAL
4
Instrumentation Circuit
Horn/Test Circuit
When the horn/test switch is pressed, the horn sounds and the following indicator lights turn on:
• Air filter service light
• Return filter service light
• Hyd oil temp light
• Charge filter service light
• Engine coolant temp light
The low charge pressure and oil pressure lights remain on because the engine is not operating. If any of the lights fail
to turn on, check the light bulbs.
Symptom: Engine oil pressure light does not turn on.
Symptom: Engine oil pressure light stays on with engine running.
Symptom: Glow plug wait light does not come on.
Symptom: Charge filter pressure light does not turn on with a blocked filter.
Probable Cause Remedy
Faulty engine oil pressure switch. With the key switch in the OFF position, check continuity between engine oil pressure
switch and ground. Continuity must be indicated. If continuity is not indicated, replace
engine oil pressure switch.
Faulty engine oil pressure light switched
power circuit.
With the key switch in the run position (engine off), measure voltage between engine oil
pressure light org wire terminal and ground. Voltage must be approximately 12 VDC.
Faulty engine oil pressure switch circuit. Check continuity between engine oil pressure switch terminal and engine oil pressure
light terminal (blu wire). Continuity must be indicated.
Probable Cause Remedy
Low engine oil pressure. Check engine oil pressure.
Faulty engine oil pressure switch. If engine oil pressure tests good, replace engine oil pressure switch.
Probable Cause Remedy
Faulty light. Check light bulb.
Faulty light circuit. Check continuity between the glow plug switch and glow plug light. Continuity must be
indicated.
Faulty ground circuit. Check continuity between ground and glow plug light ground terminal. Continuity must be
indicated.
Probable Cause Remedy
Faulty charge filter pressure light switched
power circuit.
With the key switch in the run position (engine off), measure voltage between hydraulic
filter pressure light org terminal and ground. Voltage must be approximately 12 VDC.
Faulty wiring. Connect a jumper wire to charge filter pressure switch gry/wht wire terminal and ground.
With the key switch in the run position, check the charge filter service light. If the light
does not turn on, check continuity between charge filter pressure switch gry/wht wire
terminal and charge filter service light. Continuity must be indicated.
Faulty charge filter pressure switch. Replace charge filter pressure switch.
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