Hello and Help 😂
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2nd Gear
Joined: Sep 2025
Posts: 2
Likes: 1
Hello and Help 😂
Hey there guys,
I got my truck a few months back in preparation for a big trip next summer with my horses and trailer. I’ve been rewiring and remodeling my trailer and just starting to fine tune some with my truck. I’d noticed there was some play in my 7 pin connector which I thought was the cause of my occasionally intermittent running lights, I finally got round to changing it out and realized how much corrosion there was under there. Now that everything has been replaced I’m noticing other issues.
my blue electric brake wire has a constant 12v? I know they have a sensing(?) wire so the truck knows when it is connected but surely not 12v?
I'm only getting about 6/7v to my running lights, I know they all work because I’ve tested them with my battery and my other truck and they work fine?
Currently not working at all with my ford, but they have previously so maybe I’ve wired something badly or it’s just not getting by the voltage it needs?
Read that many folks get answers and bounce but I’m here for the long haul, I’ve made it my life’s work to fix anything I’m able to on this vehicle and by golly I’m gunna need you guys to help me along the way 😂
thanks so much,
Dadless girl with a love of big old trucks 😂
I got my truck a few months back in preparation for a big trip next summer with my horses and trailer. I’ve been rewiring and remodeling my trailer and just starting to fine tune some with my truck. I’d noticed there was some play in my 7 pin connector which I thought was the cause of my occasionally intermittent running lights, I finally got round to changing it out and realized how much corrosion there was under there. Now that everything has been replaced I’m noticing other issues.
my blue electric brake wire has a constant 12v? I know they have a sensing(?) wire so the truck knows when it is connected but surely not 12v?
I'm only getting about 6/7v to my running lights, I know they all work because I’ve tested them with my battery and my other truck and they work fine?
Currently not working at all with my ford, but they have previously so maybe I’ve wired something badly or it’s just not getting by the voltage it needs?
Read that many folks get answers and bounce but I’m here for the long haul, I’ve made it my life’s work to fix anything I’m able to on this vehicle and by golly I’m gunna need you guys to help me along the way 😂
thanks so much,
Dadless girl with a love of big old trucks 😂
Lead Driver
Joined: Jun 2006
Posts: 5,676
Likes: 998
From: Near Yosemite CA
Had an issue a few yrs ago, seems some of the older 7-blade trailer wiring was different on different trucks, from my recollection, the constant 12V should go to the trailer battery, the issue I had was the trailer had been used behind a Chevy and they had wired it according to the Chevy receptacle, unfortunately I don't remember how all I rewired it... I'll have to look in my shop and see if I saved the wiring pin-out I wrote down.
What were you previously using to tow the trailer?
Oh, and Welcome to FTE!!
Yes, stick around and we should be able to help you along the way! And always report back the fix, have so many that ask questions, get answers and never follow up with what worked.
Joe
What were you previously using to tow the trailer?
Oh, and Welcome to FTE!!
Yes, stick around and we should be able to help you along the way! And always report back the fix, have so many that ask questions, get answers and never follow up with what worked.
Joe
Laughing Gas
Joined: Mar 2002
Posts: 952
Likes: 346
From: Newton Illinois
On the wire to the trailer brakes, if you are testing with a digital volt meter without a trailer connected you could well be getting voltage from the sensing circuit, try putting a old school incasedent test light on it and see what that does.
3rd Gear
Joined: Apr 2025
Posts: 3
Likes: 2
From: Halton
The blue (+) electric brake wire should be connected directly to the brake controller, this is with or without trailer connected. You should see milli-volts in between blue (+) and white (-) when brakes are not applied. You should see a voltage range from 2V-12V (13.8 ish volts if the truck is running) depending on the gain setting (full gain on the controller will provide the full 12V to the brakes (trailer) any controller gain under full will be less voltage dependent on the gain setting on the controller and brakes applied) that is for brake pedal or manual trailer only button/slider brake. If you have a constant 12V on the blue and white the wiring is not correct or you have a problem with the brake controller. There is a color difference in between the SAE or RV standards but the functions of the wires are the same. Link below for 7 flat wiring diagram
https://johnsontrailerparts.com/how-...-plug-trailer/
https://johnsontrailerparts.com/how-...-plug-trailer/
Thread Starter
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2nd Gear
Joined: Sep 2025
Posts: 2
Likes: 1
So the 12v was constant on the blue wire - I unplugged my controller and it’s gone away, it was hard wired by the previous owner to bypass the connection under the dash, curious if that had something to do with it. Will replace and see if it fixes the issue 🫡
managed to get my running lights working after finding a bad ground, hooray.
now just to figure out where the bad ground if for my right blinker on my truck. The tail light is working but the blinker is not! Anyone have any ideas?
thank you guys!
managed to get my running lights working after finding a bad ground, hooray.
now just to figure out where the bad ground if for my right blinker on my truck. The tail light is working but the blinker is not! Anyone have any ideas?
thank you guys!
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