Old Style Trailer 7 Pin Wiring

[cole3444]

I am in the process of having to replace my new 7 pin round connection trailer plug since the ground prong broke off. I have attached a pic of my wiring and wanted to ask about the center post that is for the blue brake line. Where does the blue wire attach to on the wiring for the brakes. I have a 30 amp auto reset breaker that has the brake wires from the axles attached and was wondering if the blue wire can be connected to the post with a crimped terminal.
One other question is where is the best place to connect the black wire that is connected to the 12v terminal to assist in charging my trailer battery while traveling. Thanks for any help.

[Action]

I don't understand the first question regarding the center pin connection. The reason I don't understand is the center is an aux pin or for charging the battery if you wanted to use it for that. With that said, I do know that older AS trailers have a wiring that is different from today's standard. The wiring is in different positions than today's plug connectors. Which means if you plug in an old AS trailer plug to a today's standard connector there are going to be issues with operation.

As to a connection to the TV to charge the trailer battery, the best one would be a line that is switched with the ignition switch. Running a line to the front of the vehicle in a larger gauge (like 12 gauge or larger wire) connected to a vacant power distribution connector that is switched by the ignition switch is the best. This can be done in many modern vehicles or some are already pre-wired for this in the center pin.

The second best would be to the TV battery + post directly. However disconnecting the trailer pigtail is necessary when the engine is shut off. Because the two batteries (TV & Trailer) are electrically connected and draining the TV battery from the trailer is possible.

Action

[cole3444]

I am trying to figure out what the center terminal is for, the 12v terminal pictured in the upper left is hot all the time when the cord is plugged in. The center one shows in different illustrations as the brake terminal so here I am scratching my head trying to get it to work.

[Action]

The center pin does not have a designation. It can be used for anything of your choosing.

Some trailers have back up lights. It can be used for that.
OR your choice.

Action

[cole3444]

I got the lights working the ground wire in the back side of the inside of the plug was broke inside the sheathing. E Trailer states the 12v black wire can be used for charging your trailer battery while traveling??. Center terminal will be left empty. Now hope my brakes will activate when I get ready to test them, had them wired by a trailer guy so I hope all is well. All I see is two red wires coming from my breakaway, one down to the brakes and the other to the 30 amp auto reset breaker going to the battery inside. Please say a kind word for me that it is right. Input still appreciated Jim

[rideair]

Cole,

If memory is correct, your 71-72 trailers have the connections in the front of the trailer, between the propane tanks. On that year of trailers, the center pint was used for your backup lights. If you're in a state that requires "State Inspection" they may require you to have them working.

Enjoy,

[Streamracer]

The center pin on the old round 9 pin plugs is for backup lights, yellow wire.

[guskmg]

The best way to make everything normal would be to change the connections in the pigtail junction box in your trailer. Just disconnect all the wires at the J-box, use a test light to determine each wires origin and connect them back up so the trailer socket matches the modern scheme. The schematic is usually imprinted on the cover to the TV plug.
guskmg

[cole3444]

I have all my lights working right now, my unit does not and never did have a junction box for my wires. I have backup, tail, turn, and brake lights. I plugged my cord into the truck and checked each terminal and attached the wire that went to each circuit. I have a diagram now for future issues. Will hook up my 12v terminal to help charge my battery while traveling per ETrailer article. Did find my brake wiring hot wire that comes from my axles laying inside the wall, ground was hooked up so I hope I can run the hot to the center terminal and have brakes per ETrailers drawing for 7pin round plug.