That way the flasher will not be in the circuit for the brake light switch. As an example you will.
Trailer Brake Light Kit 4 Round Incandescent With Grommet Amp Wiring
How to wire turn signals and brake lights. Just have the brake switch switch positive to both signal lights in a separate positive circuit. The 4 way system is designed so the right brake light wire and right turn signal are green. Truck stops and bike shops sell fixtures designated as two wire which means they typically use an 1157 bulb with two filaments or. The left brake wire and left turn signal are yellow. There are complicated ways to wire in multiple relays to do it and aftermarket units that will do this but there is an easier way. Visit howstuffworks to check out this brake light wiring diagram.
This is a method to display more light back there than the typical stock single tail and brake light by putting the turn signals to work as running and brake lights. This is the general configuration upon which 5 way 6 way and 7 way wiring systems build upon. If you have a single wire coming out of your rear turn signal fixtures there are ways to retrofit an 1157 type base into some of them. Connect the wire from right turn and stop to the green wire input side. Ground the white wire to the trailer frame. Brake light wiring diagram this brake light wiring diagram gives you a clear picture of where each wire goes.
Same as 4 way system listed above but adds a extra blue wire for brake signal or auxiliary power. 4 way flat adapter for truck wiring to wire third brake light of camper shell. 3 wire to 2 wire converter to combine separate brake light and turn signal circuits parts needed to connect european 7 pin to us. They will combine the brake wiring and the turn signal wiring so they will work. Side marker lights are powered by the brown wire. On the output side that will go to the trailer lights you will have the yellow wire which will now be left turn only the green wire for right turn only and a red wire for brake lights only.
White remains as the ground. They look like this. Simple wiring help brake lights running lights turn signal your signal wiring is correct. A quick and cheap way that works just as good is a tail light wiring converter for trailers. A two filament or two wire fixture is required to do this. 5 way connectors are available allowing the basic hookup of the three lighting functions running turn and brake and besides the ground one pin is available to provide support for another function.
On the 7 way wiring locate the wire for the left turn and brake and attach it to the yellow wire on the converter input side. What you have to do is make the brake light wires and the turn signal wires combine in a way that the turn signal wires can override the brake signal.