I have a 97 Ford F150 with no turn signal/flashers. I have replaced the relays and the bulbs as well as the multi-function switch with no luck. So how do I fix the problem???

Begin at the rear light socket. Use a multimeter while the turn signal is on. Check for DC voltage. If none, check the wires where they enter the socket. Still nothing, trace the wires backward toward the engine and check for a break along the way and for DC voltage at all connections. ONce you get to a connection where you have voltage the problem is either there at the connection or back toward the light. If you do not have lights at the front or rear, suspect the switch on the column. Check there for voltage also. Maybe even first.