Let me 'try' to addresss ( READ THAT -GUESS) your starting issue.
Harleys, because of their 'design', stop with ONE of them, coming up on compression. That said, when you go to 'start' it, tough sledding for the starter to 'roll it over' AND trying to fire, at same time. You let go of the button, hit it the 2nd time, Vrooooom. My 78 does it almost everytime it starts. The rest of the time, it will "FIRE" when you turn the key 'on'. "Pop". (This can be eliminated by jus' SLIGHTLY retarding the timing)
(Also, I have mine wired, first click of ign switch is Ign and brake kight, ONLY. Second click adds 'lights'. Mo' voltage for starter and ign, that way.)
This is PESHALLY troubling, when you have electronic ign, and have it set to "kick" vs "electric"
In the "electric" mode, it will turn one full revolution BEFORE the ign will 'fire'. I believe you are schmott enough, to figure out why THIS is BAD, when you are 'kicking' it to life.
Also, the Prestolite and Hitachi staters, were only .7kw. Good enough for 'stockers', USUALLY. But weak in the poop IF you've done any headwork, cubic "s, compression ^, etc.
Least expensive 1.4kw that I've found, is the Ultima .
There are Prestolite and Hitachi 1.4s, but they are just as expensive as Spyke and ALL-*****. But they work good for the guy who wants to keep the 'original' looks.
You sorta 'lost me' on your electrical testing, there. Not zacklee sure why you have that ground running to the brake res.
Trying in my head, to picture what you have, and what you were reading, there. ?????????
I run PIAA Xtreme White H-4's, 110/100w @ 60/55w in ALL our scoots (DEER !!!!!!!!!!!!!!!!!) Thusly, I run them via secondary relays, to handle the 'load'. The dimmer switch just flips the relays, NOT the lights themselves. The 'current' draw, will fry the dimmer switch, and the small handlebar wires.
I eat at least one or 2 bulbs a season (HARDTAIL - vibration/shock)
Check your ground for the headlight bulb, itself. I redo mine, IF NECESSARY, so they are grounded right at or very near, the headlight bucket/triple trees.
IF you don't have any in your box, grab some "Di-electric" grease at NAPA, Checker's, what have you. Use it on EVERY electrical connection you fiddle with. Batt cable, plug ins, bulb bases, ANYTHING. Eventually, you will have the WHOLE scoot done. Can really save you those 'qwirky' electrical/corrosion probs. BUT, JMFUO, as "ooze-all".
Gonna have to 'grind' on that testing thang, you got going on, tho. Ya lost me, there.
Dammd, that HOME GROWN is way betta than I thought !!!!!!!