Head light dimmer, no brights on the driver's side?

When the headlamps are on the low setting, they all work correctly, the headlamps and the daylight driving lights are all on, but when I switch to the bright setting the left high beam lamp doesn’t illuminate and the daylight driving light on the left goes out. I’ve discovered that if I hold the multi-dimmer switch lever halfway all the lights are on and working correctly, but as soon as I let go of the dimmer switch lever and it returns to the resting position the left lights go out. I’ve installed a new headlamp switch, a new dimmer, turn signal, cruise control multi-switch on the steering column, all new headlamps and bulbs, and I’ve checked all the grounds. I used to repair and restore Corvettes for 30 years and I’m a decent mechanic, but I’ve checked everything that goes to the lights. It’s acting as if the dimmer switch is bad, but I’ve replaced it, so as far as I can tell there’s no other switches on the column other than the multi-switch that I’ve already replaced. So, I would really love it if someone could tell me if there’s a switch I don’t know of, or if it’s something else that I’m missing.