I don't think there is a relay in the headlight circuit, but don't take that as the final word. It's good to hear that you have side marker lights because that means your Fusible Link should be good for your Headlights. Double check your headlight fuses for voltage on both sides of the fuse - referenced to ground.
Previously I typed, Incorrectly.....
The power path for headlights is: BATTERY, FUSIBLE LINK (BLACK), shunt, FUSE (20A), COMBINATION SWITCH and then LAMPS.
It should have been: BATTERY, FUSIBLE LINK (BLACK), shunt, COMBINATION SWITCH, FUSE (10A), LAMPS -- Turn Signal Dimmer Switch.
If your headlights are good (both high/low beams on both lamps being bad would be a coincidence) then the TURN SIGNAL DIMMER SWITCH that supplies the ground for either the HIGH or LOW beams may not be completing the circuit.
Also check the connectors at the lamps and especially at the radiator support bracket. Look for cut insulation through the cable shield and/or insulation at the radiator support bracket. Does your amp meter draw more current than normal when you turn your headlights on?
RLS30