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Wasn't sure what to name this topic given the problems im having...so im getting ready to trouble shoot and here's my problem(s)...Please guide me the right way

Ok so SOMETIMES when i press on the brake, my lights dim all around my car including the headlights...not every-time i brake but sometimes, Other times it enough to turn my radio off then back on for that quick second. When the brake is pressed it dimmes everything but even when holding the pedal down everything comes right back and the lights lose their dim. It can go days before doing it again and even when it does its not always every "pedal Press" now today i think i hear a faint electrical hum from my speakers but not quite sure. I bought a analog meter cause my digital cant read the quick voltage drop...(happens regardless of what's on electrical in the car)

So im planning on taking the analog to the battery and checking for voltage drop there then disconnecting the terminals when the car is running and checking it at the terminals again for voltage drop. With and without voltage load...is this right and/or any other steps i should take?

P.S - There have been nothing added to the car in years ie...radio or amps etc,etc,

Intermittent short.

After alil fuse pulling to help narrow down it seems to be connected to the "stop" fuse...when its in the lights dim for a sec but when the fuse out the lights remain fine...could it be a short off there Daninski?...or maybe to much of a load for the alternator meaning a new alt is needed?...the "stop"fuse im guessing is the brake lights right?...and the "tail" is parking lights?

There are quite a few things that could be causing problems like you described. I'm currently having similar issues to what you described.
It could be a weak battery, an extreme winter or heat could cause that. Though a weak battery would also cause hard starting (not a symptom you described), so it's not likely.
The stock alternators in our cars (and most replacements) were made by Mitsubishi. The voltage regulators on these things go out pretty quick with bad voltage. I've replaced my alternators 5x in 2 years. Recently I took my car in to have the alternator tested, and with nothing running (stereo, lights, etc.) when they put a load on... my car loses 4-600 rpm. And my lights dim, stereo flickers, etc. (my issue is a bearing going out)
Could also be a frayed wire causing a short (previous mx-3 had this). It was blowing fuses when I hit the brakes. I tracked it down to a wire with bad insulation near my trunk latch.
Could be a partially blown fuse, or a partially blown too big fuse.

Just throwing a few suggestions out there...