Hy red 53 pickup, there could be a high resistant connection somewhere in the wiring system, possibly in the dimmer switch. Measure the voltage at the headlights to verify what is available for the headlights. Verify the ground wires for the headlights, also verify that the wires to the headlights are going to the correct terminals on the headlights, one harness I installed had every connection to the headlights in the wrong spot. If everything is good, replace the headlights, hope that helps.
