Check for applicable troubles codes. There are lighting trouble codes. If your going to work on your own vehicles, at the least, you need an obd2 code reader that will read manufacturer specific codes as well as po codes.
Take the lamp connector loose, with headlamps on, check for the same voltage on all head lamp circuits, use chassis ground not headlamp connector ground.
In the diagram, the top wires are voltage, bottom wires are ground. The dimmer switch is part of the ground circuit, if you wan t to word it that way. The low beams ground through the headlamp relay in diagram. The high beams ground through dimmer switch ground. The ground wire location is the same for high and low.
Sorry it took so long.
Friday, November 9th, 2018 AT 8:13 AM