I would like to change my 4 pin trailer plug to a 7 pin trailer plug . what is the wiring diagram and how do i do it?

Trailers with electric brakes need them too. The 7-Way Trailer Plug is around 2? diameter connector that allows an additional pin for an auxiliary 12-volt power or backup lights.
https://www.ajtnt.com/Info/7-Way-Diagram
Connect to the brake controller and route the black and blue wires. Find the blue wire that comes off of your electronic brake controller. Attach the blue wire that came with your 7-wire plug to this blue wire. Locate the rubber grommet that surrounds the interior wiring harness where it feeds through the firewall.
https://itstillruns.com/wire-7pin-trailer-plug-4811994.html

https://www.narva.com.au/resources/trailer-plug-wiring-diagram

https://www.narva.com.au/resources/trailer-plug-wiring-diagram

make a 5 pin plug ---- trailer wire ---- 7 pin socket
converter cable
5 socket 7 pin round plug
Pin 2 to pin 1 left turn wire yellow
pin 3 to pin 3 Earth return to body of car
pin 5 to pin 4 right turn wire green
pin 6 to pin 6 brakes light red wire
pin 7 to pin 7 Tail light Brown wire

if it is a rectangular 7 pin then
5 socket 7 pin rectangular plug
Pin 2 to pin 1 left turn wire yellow
pin 3 to pin 3 Earth return to body of car
pin 5 to pin 4 right turn wire green
pin 6 to pin 6 brakes light red wire
pin 7 to pin 7 Tail light Brown wire
refer to narva wiring diagrams to check
could use a 12v dc probe to sus out what the pins do.
might be able to buy a converter cable from a car spare parts shop maybe or make it yourself

Depends on plug type and number of Pins used.
Is it 5 pin or a 7 pin round plug or a rectangle plug ?

http://www.narva.com.au/products/browse/wiring-diagrams

http://www.pacificnorthwestspine.com/wp-content/uploads/2015/11/dodge-ram-Wiring-Diagram-For-7-Pin-Trailer-Plug-best-detail.jpg

Hello Carol, The 7 way is for use with a brake controller and/or a trailer that has electric brakes. The 4 way flat is a basic trailer plug connector.
Connect as follows:
Green wire- Connects to the vehicles right turn wire harness & provides brake light and right turn signal on trailer.

Yellow wire- Connects to vehicles left turn wire & powers brake light & Left turn signal on trailer

White wire- Ground

Brown Wire- Tail/ marker/ license plate lights

The Blue, Red & Purple wires on the 7 way will not be used on the adapter, those are for brakes.

I hope this information is helpful.

I am guessing you mean the 7 pin trailer tow adapter.

the 7 pin RV plug itself



The 2005 trailer tow adapter wire diagrams

Here is a page online that has wiring for the 7 pin coupler. http://rvbasics.com/techtips/rv-travel-trailer-plug-wiring.html Notice that the battery charge for the trailer is on pin 4 black... Hope this helps you with your hookups. K

If you are going from a 4 pin on your trailer to the 7 pin on the truck. You need to go to parts store or a department store (ex Wal Mart) and look in trailer section and find the adapter. Thats what I did. Also Remember if your lights don't work on trailer, check the plug to make sure its tight or check the fuse under your drivers side rear seat for that fuse box.

Here's one
CAV CIRCUIT FUNCTION 1 Z13 12BK GROUND 2 B40 12LB TRAILER ELECTRIC BRAKE OUTPUT 3 L76 12BK/OR TAIL LIGHT (Trailer Tow Relay in PDC) 4 A6 12RD/TN* FUSED B(+) (40A, Always Hot, F8 in PDC) 5 L63 16DG/RD LEFT REAR TURN SIGNAL TRAILER TOW 6 L62 16BR/PK RIGHT REAR TURN SIGNAL CONNECTOR 7 L1 16VT/BK BACK-UP LAMP FIGURE 1: 7-Terminal Trailer Tow Connector

I believe you can look up the manufacturer of the trailer plug kit and find the wiring diagram there. On alot of the trailer plug kits, they have pics and diagrams in the package. The 7 pin plug (truck side) is available with the pig tail set up that plugs directly into the wiring harness for the lights. Then all you would have to worry about is the 2 wires for the electric brakes.