Case IH 1523 – UCM (Universal Control Module): Left Brake Light Shorted To Power

The electrical circuit controlling the left brake light is receiving voltage when it should not be, meaning there is a short circuit connecting the brake light's signal wire directly to a 12V power source, or there is an internal short within the light assembly itself.

• skid steer
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• SR130
• SR175
• SR200
• TR270

1. 1

   Visually inspect the left tail light assembly for physical damage, cracked housings, or water intrusion, which commonly causes internal shorts.

2. 2

   Trace the wiring harness from the left brake light back to the UCM. Look for pinched wires, chafed insulation, or areas where the brake light wire might be rubbing against a constant power wire.

3. 3

   Disconnect the left brake light pigtail. With the machine ON but the brake pedal NOT applied, use a multimeter to check for voltage at the brake light signal pin on the harness side. If 12V is present, the short is in the wiring harness or the brake light switch.

4. 4

   Inspect the brake light switch to ensure it is not mechanically stuck or internally shorted, which would send a constant power signal to the UCM/lights.

1. 1

   Disconnect Power

   Disconnect the machine's battery to prevent further electrical damage or blown fuses during the repair.

2. 2

   Isolate the Component

   If your diagnostic tests revealed 12V at the connector when the brake was off, locate the damaged section of the wiring harness. Repair the wire using proper splicing techniques and heat-shrink tubing, or replace the affected harness section.

3. 3

   Replace the Assembly

   If the wiring tests fine but the code persists when the light is plugged in, the tail light assembly is internally shorted. Remove the mounting hardware, disconnect the pigtail, and install a new tail light assembly.

4. 4

   Reassembly and Testing

   Reconnect the battery. Turn the machine's key to the ON position and clear the fault codes from the UCM.

5. 5

   Final Verification

   Press the brake pedal to ensure the left brake light illuminates properly and verify that fault code 1523 does not return.