Had headlights, then high beam only, now nothing

Update:
I have checked about all of the wiring, under the hood. I have checked the alternator output & monitored the battery voltage, when I turned the lights on. Remembering an issue I came across, when I worked years ago, at a VW dealership. I was checking the car over, as part of a Pre Delivery Inspection. While checking the lights, I put it on high beam and before I could put it back on low beam, it happened automatically! And then back up on high beam! I turned the lights off and another mechanic saw what happened and told me that he had the same basic thing happen to him once & it turned out to be a single light bulb, with a problem. That bad bulb was causing feedback & triggering the dimmer switch. I checked the one I was working on and found that the left rear Brake/turn signal bulb was the problem. The upper element had somehow, come loose on one end and dropped down onto the lower element, causing the feedback. Sorry about my explanation, being so lengthy, just trying to make sure that the intent was obvious. now, I have checked the headlight bulbs (again), park/turn bulbs, tail lights (tail, turn/brake, backup & license plate light. The license plate light bulb was blown. Now, I am putting things all back together enough, to see how it goes. But, before I do, I am not happy with the way the stereo was put in and haphazard wiring of it. So, I am going to pull it,& make sure everything in that area looks to be okay. Thank you all, for your patience. My patience, with this, is growing thin, especially with all we have going on, presently.