I'm hoping you guys could help me figure out how to install a 7-pin trailer light plug on my 78 F150 Super Cab 4 x 4. I have the trailer brake controller the seven pin head and a whole spool of multi colored wires all I really need is to figure out how to attach it to the factory harness without nuking the factory headlight switch.

 

Here's what the factory wiring diagram says: for rear lights
Blk/rd= backup lights
Black= side marker, tag lights (on styleside)
Brown=tail lights, tag light (on flareside)
green= RH stop and brake
Yellow/blk= LH stop and brake

Rear light wiring
BROWN: running light circuit
YELLOW with BLACK stripe: driver-side stop/turn
GREEN: passenger-side stop/turn
BLACK with RED stripe: backup lamps

Flat bed wiring…
Brown= Run Light
Green= Brake light- L
Yellow= Brake Light- R

7 pin diagrams. https://www.ford-trucks.com/forums/1...l#post14696878

By now I am sure they make a plug in "inline" wiring adapter for the trailer.

 

I used this kit from Etrailer. Brake/turn/running lights tie into the rear harness for the taillights... just like a simple 4 pin harness Heavy leads for brake power and trailer accessory power (10 gauge) run up to the engine compartment to tie into the battery and brake controller.

It does have some diagrams that are helpful. I did need to buy some additional 10 gauge wire to get the routing I wanted in the engine compartment.

https://www.etrailer.com/Accessories...ler/ETBC7.html

 

I like to run the trailer turn and tail lights through relays, to avoid the extra load on the headlight switch.
Trigger the relays (left turn, right turn and tail) by the appropriate leads and power the trailer lights from new, fused circuits. All the wiring is in the engine compartment and the new components (fuses or breakers, relays) can be mounted under the hood, allowing you to run a new "trailer wiring loom" to the back of the truck, and trailer plug.



Good luck