electrical problem

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Aug 19, 2019 | 12:15 PM

pdarby

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Joined: Nov 2013

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electrical problem

I have a 2017 F350KR DRW 4x4. When I test the trailer 7 way plug with a 7way tester I get no light in the 12V position, which I assume means the truck is not charging the trailer batteries. Second when I apply the brakes all I get on the tester is a very dim flickering light on the BK position. Ive checked the fuses and they seem good, don't know how to check the relays though

Aug 19, 2019 | 12:17 PM

HRTKD

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Joined: Oct 2015

Posts: 19,676

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From: Wyoming

On my 2017, all I had to do was press the brakes and I had power to the trailer. Others have reported that more was needed, like closing the driver door and putting it in gear.

Aug 19, 2019 | 12:26 PM

ford390gashog

Fleet Owner

Joined: Jan 2004

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From: Brentwood,CA

The 12v is only hot when the truck is running, the brake wire will only go hot with a trailer connected as the smart trailer tow junction box needs to see the resistance of the trailer.

Aug 19, 2019 | 12:32 PM

pdarby

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does that mean the brake wire will not go hot with the tester plugged in?

Aug 19, 2019 | 04:51 PM

2019er

Laughing Gas

Joined: Oct 2018

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From: NC

Saw on another thread here just a few minutes ago, was happening if you enabled police mode through Forscan. Does that apply to your case?

Aug 19, 2019 | 11:16 PM

bobv60

Fleet Mechanic

Joined: May 2011

Posts: 1,866

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From: Rainier OR

This has happened to others, the tester will not work correctly on the newer trucks.
You wont get power to the B+ untill the brakes are pressed and the truck is moving.
Same with the trailer brakes. Needs to sence there is a load before they come on.