Instrument bulb lighting...still dim

The fact that your dash light dimmer switch (for the instrument lights, when you rotate the headlight switch) is intermittent, and only works kind of in one position is a dead givaway that YOU NEED A NEW HEADLIGHT SWITCH. They are reasonably cheap at auto parts stores, and can be installed in less than 30 minutes. There is a round spiral of wire that runs on a wiper contact, and rotates with the knob. It gets old and broken, only working in one spot. It is essentially a variable resistor that varies the voltage to the dash lights. Put a new switch in the car and solve your dim dash light problems.