Hi,
I have a 1977 F-150 Custom with 351m and 4x4.
I bought a new trailer this weekend to pull my boat and it has the 5 pin trailer electrical harness. Now the truck only has a 4 pin. The extra one on the trailer, from what i understand is to allow the trailer to be reversed since it has disk trailer brakes. I imagine there is an electrical solenoid on the trailer that keeps the brakes from applying when you go to back up.
Now my question is: What is needed to make this work with my truck? Is there an adapter for the pigtail or do I need to connect that extra wire on the trailer to my reverse lights on the truck somehow? Thanks for any help.

 

Looks like I need to wire in a 5 pin harness to the truck and connect the extra one to the reverse lights. Is this correct?

 

Never seen anything like youre describing................ Normally, trailer wiring consists of the following circuits:
Left turn / Brake light
Right turn / Brake light
Tail lights
Trailer brake feed
Ground
B + Hot wire for interior lights
Possibly a switched hot lead for charging a battery on the trailer/ or for reverse lights on the trailer.
A lot of times noone runs the ground wire, thinking it will ground thru the ball, but I highly reccomend utilizing the ground. It prevents a lot of problems

 

You are absoultely right. You need to get a 5 flat plug for the truck hook up all the colors just like your current 4 flat and run the extra wire to the reverse. The nice thing is that your other trailers that use the 4 flat will usually plug right in to the 5.

 

Thanks for the help. I got it fixed last night. Theres an adapter that they sell at parts stores for this. You just plug it in and run the extra wire to your reverse light circuit on the vehicle.