If they both come on at normal intensity on all 4 on high it narrows it down. Ground has to be good and power feed to switch is good. Test light the red blk wire beyond the switch. Areas of suspicion are the dimmer connector itself, the gang plug at the firewall (most likely as it is the only other break and subject to corrosion) or of course at the lights themselves. I have to ask (since I have come across it 1/2 dozen times over the years), are you sure you don't have 2 burned out low beam elements? Never overlook the obvious. My bird is at the shop or I would look but it may not be a gang plug. It may be a regular connector beyond the firewall but the principle is the same. If you get to the point where you are looking for that connector and I will look at mine and give you the exact location but follow the light wires back and it will be obvious.
