No Power to Trailer Interior Light with 2019 Ford F-250

Updated 03/14/2023 | Published 03/13/2023

Products Featured in This Question

40 Amp In-Line Circuit Breaker - Perpendicular Mount Bracket

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10 Gauge Wire - Red Primary - Per Foot

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Question:

We recently bought a 2019 F250. When hooking up the 7 connector plug to our horse trailer, the lights on the outside of the trailer, running lights, turn signals, brake lights, etc. all work but the lights on the inside of the trailer to work operated by a switch inside the trailer. Hooked the same trailer to 3500 Chevy and ALL lights worked. Everything also worked on my old 2004 F150. Reading several threads, I put the 30 amp fuse in slot 27. Here is the interesting part. I see several mentions about the Trailer tow battery charge relay, slot 37. I purchased the relay from Ford but when looking where relay 37 goes there are no connections for the relay to plug into. There is a slot for 37 just no metal connections. Any additional information you can provide on what I can do to get the internal lights would be appreciated. Thanks.

asked by: Trey B

Expert Reply:

The Ford Smart Tow System on the 2019 Ford F-250 won't send power to the battery charge line circuit until the vehicle is in motion and gear shifting. The battery charge line circuit is what is powering the interior lights on the trailer. Therefore, you won't be able to use the lights without installing an on-board battery on the trailer or bypassing it. There isn't anything wrong with the truck, that's just how the system is designed. I am not aware of any way to change the setting for this.

In regards to bypassing, you'd basically wire a battery charge line circuit of your own from the truck battery to the trailer connector using part # DW02508-1 and part # 9510.

expert reply by: Conner L