Ford Super Duty Upfitter Auxiliary Switch Module (HC3Z-14G372-AG / HC3T-14G372-AG)
Updated June 20, 2026
The Ford Super Duty Upfitter Auxiliary Switch Module (also referred to as the multifunction chassis ECM or upfitter interface module) is the electronic control unit that manages the four upfitter switches mounted on the dashboard of 2017–2024 Ford F-250, F-350, F-450, and F-550 Super Duty trucks. Located behind the glove box, this module receives switch inputs and routes battery power to the corresponding auxiliary circuits, enabling safe and convenient control of aftermarket equipment such as work lights, winches, air compressors, and plows.
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Function and Operation
The upfitter switch module acts as a multiplexed relay center that communicates with the vehicle’s CAN bus. When a driver presses an upfitter switch, the module detects the request and energizes the appropriate output circuit, supplying fused battery voltage to the pre-wired pigtails under the hood or in the cab. The module also supports programmable switch behavior (e.g., ignition-on or battery-direct) and can be configured via Ford diagnostic software. This design eliminates the need for separate relays and aftermarket wiring, providing a clean, factory-integrated solution.
Vehicle Fitment
This module is designed exclusively for Ford Super Duty trucks built between 2017 and 2024, including the F-250, F-350, F-450, and F-550 models. It is a direct replacement for the original part and is identified by Ford service part number HC3Z-14G372-AG (engineering number HC3T-14G372-AG). Some listings also reference compatibility through 2022, but the module has been verified for use through the 2024 model year. Always confirm your vehicle’s build date and existing module part number before replacement.
Common Failure Symptoms and Diagnosis
Symptoms of a failing upfitter switch module include one or more auxiliary switches becoming unresponsive, intermittent operation of connected equipment, or no power at the auxiliary pigtails. The module may also cause a “Service Upfitter Switches” warning on the instrument cluster. Diagnosis begins with checking the module’s power and ground circuits, inspecting the connectors for corrosion or bent pins, and using a scan tool to verify CAN communication and retrieve fault codes. A known issue is internal relay failure due to moisture ingress or overloading the circuits beyond their rated capacity.
Replacement and Installation Notes
Replacing the upfitter switch module is a straightforward procedure: disconnect the battery, remove the glove box (typically by releasing side stops and lowering it), unplug the wiring harness from the module, and remove the mounting screws. Install the new module, reconnect the harness, and reinstall the glove box. After replacement, the module must be programmed with the vehicle’s configuration using Ford IDS or a compatible scan tool to ensure the upfitter switches function correctly and the correct circuit ratings are applied. Without programming, the switches may remain inactive or trigger warning lights.
