Main dipped headlights not working

OK let's step back, referring to your own hand drawn diagram. It seems to me we have a basic power problem that is affecting the ENTIRE interior of the car.

This is based low? readings at the headlight / dimmer switch which is "most directly" supplied.

Also, your 4X / hazard flashers are supplied off the "hot" buss in the fuse panel, and that wire is also pretty "directly" fed.

So you need to backtrack from there

What have you changed? from original in the power path to the light switch / ignition switch?

Did you eliminate the bulkhead connector terminals for the "big" red? If not I would start there and at the fuse link.

REMEMBER you cannot check this stuff WITHOUT A LOAD. So you need the lights on, etc, to load down that circuit.

How did you bypass the ammeter? Check that connection!!! Between the old "big red" and the "big black" at the ammeter (originally)

If / when you start to get this straightened out, and since you have a new fuse panel, I would try and add some things to "fused." Wipers for example.

If / when you find the trouble at the headlight switch, and if the ignition switch is still low, "it's simple." You need a load on the switch, heater, ignition, signals, something. With that load, check the switch "coming in" and "going out" Should be obvious if the switch is at fault.