Do you have a DVOM..or can you borrow one?
If so, start and warm your car..let it run at least 5 minutes, to replenish the load from the "cold start" your starter took out of the battery..
With the engine running and no load on the system..everything off, set your DVOM for DCV, Scale for VX50 , and measure the battery voltage, it should read between 13.95 and 14.4 Volts. If not, and the running check is 12 volts or below, your alternator is headed south..rebuild or replace..
If it IS between 13.96 and 14.4, then load the system with the headlamps..let it run a few seconds and measure again, if the voltage is below 13,95 the diode regulator is going south..rebuild or replace..
You can either buy a new one , ($39.00 to $250) or get a kit, ($20) and rebuild it yourself...I advocate the rebuild..you already know it's right for the car, and Fits..and you'll end up with a much better unit then over the counter parts today..(Poor QC on new Electrical Parts now a days. many out of the box failures) If you decide to do that, I can give you step by step directions , and there is an article on the WIKI, I wrote, you can read. It's easy to do , only takes a few hours of your time...
If you find the Alternator to be good, and the grounds are good, you could have an issue with the switch gear going out..
The Headlamp switch as well as the High Low beam switch may have burned contacts as well as loose terminals..
If that is the case, you should consider running headlamp realys..This takes the load OFF the switch gear and AT LEAST doubles the headlamp brightness..A Good Saturday project!
BTW:Good Post! :thumbup: