First check the voltage at the battery terminals. With the engine running at 1,000-1,500 RPM it should be around 7.5 volts. Then check the voltage at the headlights. It should be very close to the same voltage, at least 7V. If it's not, find the high resistance connection- - - -ammeter, headlight switch, dimmer switch, junction blocks, etc. The dimmer switch is by far the most likely choke point. The simple solution is to install a heavy hot wire (#8 or so) from the battery to near the headlights, and use a relay from there to provide a low-resistance high/low beam circuit. Use the dimmer switch to trigger the relay. Also be sure the headlights have a very good ground circuit.
Jerry
