First off wire is wire... The electricity flowing through it does not know what color the insulation of the wire is... Color is for people.
4wire (flat- bonded together) is simplest to work with....
Generally with 4 way flat wire the WHITE is used for ground, Yellow is Left turn/Stop lamp, Green is Right turn/Stop lamp and Brown is Tail/Marker lamps.
It could be that your lamps are Stop/Turn - Tail lamps and each wire represents each function... Check inside of lamp assemble to see if there is metal strap from lamp sockets to screw/bolt locations. Most of these lamps are internally grounded ( designed to be mounted on metal trailer frame) and only the two light wires extend outside housing. Tail lamp assemblies are designed to be mounted to metal frame, and if you have them mounted on wood, you will need to bring a ground wire to lamp assemblies (just extend White wire to lamp mounting studs/bolt/screw)
Upon examining some lamps I have here, it appears the Green wire is Stop/Turn and the Brown wire is Tail/Marker lights... Your results may vary.
When hooking them up remember Stop/Turn is bright, Tail/Marker is dimmer...
IF you have it wrong, just reverse wiring.... No harm done.
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