I have an 83 w150 and the lowbeams work but the high beams dont, I've heard it could be the relay but I'm not sure where it is, I've also heard it could be the switch but I'm looking for other solutions before I replace it

 

if you want to be cheap and be sure it is the dimmer switch then just turn the headlights on and jumper the switch using a paperclip or any other small piece of wire. doesn't matter which 2 wires you connect at the switch. eventually you will get the highs to turn on if it is the issue since there is nothing at the connector to short out. 1 is power in let and then 1 goes to lows and other goes to highs.

 

It's probably either the high/low switch on the floor next to the kick panel or both high beams are burned out. Considering it's where muddy and wet shoes sit in the rain, it's usually the switch.