Converting to 4 flat ???
If you're converting to a 4 flat plug, you'll need a trailer wiring converter...
So your 7 pin has wires for separate brake lights, tail lights, L flasher, and R flasher.
The 4 pin gives you tail lights, and combines the brake light and flasher into one.
So you end up with a wire for:
both tail lights
R flasher and brake light combined
L flasher and brake light combined
The trailer wiring converter electronically overrides the brake light with the turn signal pulse. So when you are driving and step on the brakes with the flashers off, both brake lights come on (glow). But, when you have a flasher on and step on the brake, the brake light does not interfere with the flasher, since they both use the same bright element in the bulb. In this case the flasher will continue flashing and the opposite brake light will be the only one of the 2 brake lights glowing. Pretty simple really.
Hope this helps.
Uncle "Richard" Douglas has a Land Rover with big wheels that never gets stuck... until he breaks something so it won't go. Uncle Douglas always breaks something. - Anna Crowther at the Conclave 2012 (AKA Carburetor Neck)