Case IH 1078 – Transmission / Cab Control Module (CCM) / Armrest Panel Hub (APH): Right external fender switch short to Vbat

The circuit for the right-hand rear fender switch—which allows the operator to control the rear PTO or the electronic draft control (3-point hitch) from outside the cab—is receiving unintended battery voltage (a short to power).

• MAXXUM T4E
• Puma 140
• Puma 210
• Maxxum Series (Tier 3 and newer)
• Farmall 85C
• Farmall 95C
• Farmall 105C
• Farmall 115U
• Magnum 235-340

1. 1

   Disconnect the right external fender switch. If the fault code changes from 1078 to 1077, the short is internal to the switch itself. If code 1078 remains, the short is in the wiring harness.

2. 2

   Trace the wiring harness from the right rear fender switch back to the transmission/cab controller. Look for chafed insulation, pinched wires, or melted loom where the switch signal wire might be rubbing against a 12V power supply wire.

3. 3

   Using a multimeter, test the switch inputs (e.g., PTO supply/dog supply wires 2050E Green or 2050 Green/Red, and switch signal wires 2056 White or 2056 White/Red/Yellow) for continuity to battery voltage when the switch is in the neutral/off position.

1. 1

   Power Down

   Turn off the tractor and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Access the Switch

   Locate the right-hand side rear fender switch housing. Remove the retaining screws or clips holding the switch panel to the fender.

3. 3

   Disconnect and Remove

   Unplug the electrical connector from the back of the switch. Depress the retaining tabs on the switch body to push it out of the fender bezel.

4. 4

   Repair or Replace

   If the diagnostic checks pointed to a harness short, repair the damaged section of the wire, apply heat-shrink tubing, and secure it with a new wiring clip (OEM Part # 47505757). If the switch failed internally, install the new OEM replacement switch into the fender bezel until it clicks into place.

5. 5

   Reassembly

   Reconnect the electrical harness to the switch. Secure the switch panel back onto the fender.

6. 6

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use the tractor's diagnostic menu or a service tool to clear the inactive 1078 fault code. Test the external PTO/hitch function to verify the repair.