Re: Need help with the high beams
If there is a high resistance, like a worn-out switch or a wire that is corroded, it will still show 12 volts at the lamp socket with the minuscule draw of a meter or test lamp. Test it again when it is supplying current. Pull the connector slightly off of a bulb, but not enough to make the lights go out. Stick the meter probe onto the connecting blades when the light is supposed to be on. A loss of voltage will show you if a high resistance is burning off the voltage when the bulbs start drawing amps.
Depending on the type, you may be able to make the same tests at the dimmer switch connection. If 12 volts comes out on the low beam pin, and little or nothing when selecting high, it's definitely the switch. If there is plenty of high beam voltage out of the switch with the bulb connected, but none at the headlight, the wiring is suspect.
In that case, feel along the wire for a bulge, a hard spot, or an area that won't bend as easily as the rest of the wire. If you find such a spot, chances are that there will be green powder instead of metal inside there. All it takes is a pinhole in the insulation at a wet location.
I would still suspect a worn switch is the most likely culprit.
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.