Case IH 520577-03 - BCM – BCM: Short circuit to B+ on the rear right turn light circuit

The electrical circuit controlling the right-hand rear turn signal is receiving constant or unintended battery voltage (12V) when it shouldn't be, likely due to a wiring short, a melted connector bridging pins, or an internal short within the light assembly.

• MAGNUM AFS Connect
• Magnum 180
• Magnum 200
• Magnum 220
• Magnum 240
• Magnum 250
• Magnum 280
• Magnum 310
• Magnum 340
• Magnum 380
• Magnum 400

1. 1

   Inspect the rear right tail light/turn signal assembly for physical damage, water intrusion, or melted plastic that could cause an internal short

2. 2

   Trace the wiring harness from the rear right turn signal back to the BCM, looking for pinched wires, rubbed insulation, or chafing against a constant power wire

3. 3

   Disconnect the tail light and the BCM connectors to check for corrosion, moisture, or bent pins that could bridge the turn signal pin to a 12V power pin

4. 4

   With the turn signal switch OFF, use a multimeter to check for voltage at the turn signal connector. If 12V is present, there is a short to power in the harness

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the tractor's battery to prevent further electrical damage or accidental sparking.

2. 2

   Isolate the Short

   Disconnect the rear right turn signal assembly. Reconnect the battery and test the circuit with a multimeter. If the short to B+ disappears, the fault is internal to the light assembly. If the short to B+ remains, the fault is in the wiring harness between the light and the BCM.

3. 3

   Repair Wiring or Replace Component

   If wiring is damaged: Splice and repair the damaged section of the harness using weather-sealed heat shrink connectors, or replace the affected harness section. If the light is faulty: Unbolt the rear right tail light assembly and install a replacement unit.

4. 4

   Reassemble and Clear Codes

   Reconnect all harnesses. Power on the tractor, clear the inactive fault codes from the AFS Connect display, and test the right turn signal to verify the repair.