Hep with with wiring in truck ? The one turn signal is not working bought new bulb still nothing ? Checked with meter getting 12 volts I bought new socket to replace but wires are confusing me the new socket has red , white and black so how do I cut wires and attach the colors

 

Ford standard colors are:
Bk - return/ground (the outer shell of the bulb)
Br - parking/marker lights (the brighter filament in the bulb)
Wh/LB - RHF turn (the brighter filament in the bulb)

So figure out which of the socket's wires goes to its side terminal, and connect that to Bk. Then turn on the parking lights & touch the Brown truck wire to one of the other socket wires. If the bulb comes on dim, connect Br to that wire. If the bulb comes on bright, connect Br to the other.