My truck did not have a tow package and was not intended to have one and therefore did not have a junction connector like most trucks. I have mounted a seven blade hook up to the bumper and have everything but the electric brake pin hooked up. This is where I have become stumped. Do I take my brake light wire and splice it to the electric brakes pin or do I need a relay or something in between? Additionally, The seven pin that I have mounted to my bumper has a four pin right next to it. Using the 4 pin does not give me brake lights on my trailer. How do I properly splice this in to provide brakes to seven pin trailers and brake lights to four pin trailers?

  • Welcome to Motor Vehicle Maintenance & Repair! Commented Mar 21 at 20:43

1 Answer 1


The electric brake pin is supposed to be used with a trailer brake controller. It's a device which uses a feed from your vehicle brakes and can vary the output to tell the trailer brakes how much braking force to apply to the trailer brakes. If not done this way, the trailer brakes would lock up every time you stepped on the brake pedal (if you tied this into your brake lights).

If the trailer you're going to be towing doesn't have brakes (relies totally on the braking power of the vehicle) then you don't need one of these. If you're ever going to be towing something which does, you'll definitely need one.

As far as the brake lights to the 4-pin, if it isn't providing brake lights, you didn't connect the wire which would give you that. You need to figure out which wire isn't hooked up and that's the one you need to connect tie into the brake lights. You should have received a wiring diagram with the plug you got which should help you figure out which one is the one you need. It would not be the one which is for the trailer brakes.

Something else you could do about the 4-pin is test it to see if you're getting power through the brake light pin when you press the brakes. You can do this with a multimeter. If you're getting power, but no lights on the trailer, it could very easily be it isn't getting a good connection. If so, cleaning both sides might help.

  • At least on my truck, adding the brake controller was quite easy, with a place to plug it in readily available under the front dash.
    – Jon Custer
    Commented Mar 21 at 21:35
  • I do recall it being a pain in the neck looking at the various wiring diagrams - you have to make it perfectly clear to yourself if the diagram is looking at the socket on the car or the plug coming from the trailer cable... But the multimeter helps sort it all out...
    – Jon Custer
    Commented Mar 21 at 21:37
  • On a four pin there isn’t a brake light according to everything I’ve been reading. According to everything I’ve been reading it’s left turn signal, right turn signal, tail light and ground. That’s actually how I have it hooked up and the turn signals work, tail lights work, and running lights work.
    – Timberwolf
    Commented Mar 22 at 21:05
  • However, I did find some thing that leads me to believe that I should be wiring my brake light to both turn signal pins as well. What I don’t like about that idea is I don’t want any electrical backflow a short or an over volt and blow Something. It makes sense though because the turn signal just makes the light brighter just like the brakes should.
    – Timberwolf
    Commented Mar 22 at 21:07

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