Duster Headlights not working even with power?

Short answer: Get a relay kit from Crackedback or Slantsixdan. Of course that still needs the + signal from the switch to operate the relay.
In the meantime... Did you try both high and low beams? If nothing works its either the ground, or the + side before the switch. I one works and not the other, the problem is in the + side after switch. Check both connectors to see if same. If nothing worked, put the meter neg in the connector neg and check both low and high + side. If you don't get anything, move the neg to the battery. If that works, its in the neg side and you need to work through the circuit till you find where it loses it. If moving neg meter lead doesn't change anything leave it on the battery and work through the + side till you find the voltage. Then move the neg lead back to the headlight connector. Voltage still there? Neg side is good and problem is between where you found + voltage and the connector at headlamp.