No trailer brake lights - Not Connector
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5th Gear
Joined: Sep 2008
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No trailer brake lights - Not Connector
Trailer brake light problems. My trailer brake lights do not work. Left and right turns on the trailer work, as do the regular running lights. At the fuse box in the cab, fusebox #13 is good. Under the hood, Fuses 20 and 22 are good. I can test light power on fuse 20 and 22 when the turn signals are on, but not when the brake pedal is pushed. all 3 brake lights on the EX are working. Does the switch at the brake pedal have 2 separate 12V outputs? One for the Ex and one for the trailer? Thanks
PLATINUM SPONSOR
Joined: Feb 2026
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That’s a weird one 
If your truck’s brake lights are working but the trailer isn’t, I don’t think it’s the pedal switch. It usually feeds both. Might be something with the trailer wiring or the connector not getting the brake signal.
I’d probably check the 7-pin plug for power on the brake pin when you press the pedal, and also make sure the ground is solid. Trailer wiring issues can be sneaky like that
If your truck’s brake lights are working but the trailer isn’t, I don’t think it’s the pedal switch. It usually feeds both. Might be something with the trailer wiring or the connector not getting the brake signal.
I’d probably check the 7-pin plug for power on the brake pin when you press the pedal, and also make sure the ground is solid. Trailer wiring issues can be sneaky like that
Lead Driver
Joined: Aug 2022
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From: Oologah, OK
I always put the 4-way flashers on to Test for Brake light circuits.
it is one and the same.
or, use a locking stick to hold the brake pedal down,
it is one and the same.
or, use a locking stick to hold the brake pedal down,
Fleet Mechanic
Joined: Jan 2023
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The trailer brakes and turn signals go through two relays. If the turn signals on the trailer are working, the relays are working. When you press the brake pedal, two outputs from the multifunction switch send power to the 1. Trailer relays and 2. The bulbs on the back of the EX. It's possible the connection in the multifuction switch is broken and the brake signal is not going to the trailer relays. The A and B connections in the diagram are brake and turn signal "signals" coming from the multifunction switch.
Find the relays and see if you can hear them click with the brakes and turn signals. It's difficult to measure volatges at the relays.
You may need a new multifunction switch...but take some measurements first.
https://lemon-manuals.la/Ford/2003/E...1%20to%2095-4/
Find the relays and see if you can hear them click with the brakes and turn signals. It's difficult to measure volatges at the relays.
You may need a new multifunction switch...but take some measurements first.
https://lemon-manuals.la/Ford/2003/E...1%20to%2095-4/
Last edited by Don Ridley; Apr 30, 2026 at 09:15 PM.
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