John Deere – 1023E, 1025R and 1026R – Regulated Voltage Output Test

[1] – Park machine safely. Key switch OFF.

[2] – Remove surface charge from battery by turning on the headlights for 1 minute.

[3] – Set multimeter to measure DC voltage.

[4] – Connect meter black lead to battery negative (–) terminal.

[5] – Connect meter red lead to battery positive (+) terminal.

[6] – Start and run engine at FAST idle.

[7] – Read meter several times during 5 minutes of fast idling. Voltage should remain at specification.

a. If the DC voltage remains below the minimum specification: Check belt tension. Test power cables between alternator and battery. Check for power at the regulator connector Red wire. Inspect alternator for worn or damaged brushes, slip rings, shorted diodes, or burnt wires. If all appears OK, replace voltage regulator.
b. If the DC voltage goes above the maximum specification, replace the voltage regulator.

Alternator outputs exceeding 20 VDC shuts down all instrument control cluster outputs and stops machine operation.