2020+ Super Duty Aux Switch Always-Hot Configuration — Fuse-Based Setup Explained
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Quick Summary
On 2020+ Ford Super Duty trucks, factory aux (upfitter) switches are key-on by default. This means the aux circuits only receive power when the ignition is on.
However, Ford provides a factory-supported method to configure certain aux switches to be always hot (battery powered) by changing fuse positions in the under-hood upfitter fuse box. This is a physical fuse configuration, not just a software or BCM setting.
Understanding this distinction is critical when wiring accessories that need power with the truck off.
Factory Default Behavior
From the factory, all aux (upfitter) switches on 2020+ Super Duty trucks are configured as key-on. Accessories wired to these circuits will not receive power unless the ignition is in the on or accessory position.
This default behavior is intentional to prevent unintended battery drain and to ensure accessories shut off with the vehicle.
Which Aux Switches Can Be Always-Hot
On most 2020+ Super Duty trucks equipped with factory upfitter switches:
- Aux switches #5 and #6 are designed to support always-hot operation
- Aux switches #1 through #4 are not designed to be always-hot using factory fuse positions
Aux 5 and 6 are typically higher-current circuits and are the only switches Ford provides a factory method to configure as battery hot.
How Always-Hot Is Enabled (Fuse-Based)
Always-hot behavior for Aux 5 and 6 is enabled by changing fuse positions in the under-hood upfitter fuse box.
This process typically involves:
- Locating the upfitter fuse block under the hood
- Moving the designated fuse or fuse selector for Aux 5/6
- Changing the circuit feed from ignition-switched to battery hot
This is a physical configuration change. It does not require BCM programming or software changes.
Exact fuse locations and procedures can vary slightly by model year and trim, so owners should always reference their specific upfitter documentation and verify with a multimeter.
Common Causes of Confusion
Many owners report confusion around always-hot behavior due to:
- Assuming aux switches are always-hot by default
- Relying on printed documentation that differs by year
- Not realizing Aux 5/6 require fuse changes
- Assuming BCM programming controls hot vs key-on behavior
- Differences after dealer service or fuse box work
In most cases, unexpected behavior is caused by fuse configuration, not software.
Best Practices
To avoid issues:
- Verify fuse configuration before wiring accessories
- Test Aux 5 and 6 with a multimeter for battery hot vs key-on
- Do not assume always-hot behavior without confirming
- Plan accessory wiring based on confirmed power behavior
- Re-check fuse positions after dealer service
Model Year Notes (2020+)
- 2020–2021: Fuse-based always-hot configuration for Aux 5/6 is well documented
- 2022–2024: Same fuse-based method applies, though fuse box layouts may vary
- Factory documentation may differ by build date and trim level
Always verify using your specific upfitter guide and vehicle fuse box labeling.
Sources & References
These sources document fuse-based always-hot configuration for Aux 5 and 6 on Super Duty trucks:
FordTremor.com — Upfitter switches always hot (Aux 5 & 6)
https://www.fordtremor.com/threads/upfitter-switches-always-hot.8141/
Ford-Trucks.com — Upfitter switches hot all the time (Aux 5 & 6)
https://www.ford-trucks.com/forums/1718872-upfitter-switches-hot-all-the-time.html
Ford Fleet Documentation (referenced in multiple forums)
Documents Aux 5 and 6 battery hot configuration via fuse selection
OTC Perspective
Most always-hot issues we see are caused by incorrect fuse configuration or incorrect assumptions about factory defaults. Aux switches are key-on by default, and only Aux 5 and 6 are designed to support always-hot operation using factory fuse positions. Verifying fuse setup first prevents unnecessary rewiring and troubleshooting.