1973 yamaha dt3. I have rewired and installed Vape on this bike. All circuits are working, but I have not connected the blue Vape wire to the black wire with a white stripe running to the switch. Vape instructions say to "splice" the blue wire to to the Black wire with a white stripe, like maybe you don't disconnect the black and white wire from the black wire to which the black and white wire is now connected, you just "splice" the blue wire into that circuit, I think that black wire is now out of the picture and you just directly connect the the blue wire to the black wire with a white stripe, but not sure.

DEET ( if I recall correctly) rewired my headlight/flasher switch.  The high beam does not come in it's ususal position, it does not come on until I slide the switch up toward the low beam position, then, with very  slight movement toward the low beam, the high beam cuts off, the low beam comes on when in the low beam position. Something is out of whack in there, but as I understand it, there are small springs and ball bearings in there, concerned that if I start taking it all apart I will wind up with a switch that doesn't do anything. Is it mess getting that switch back together, or best to just leave it alone?

Without knowing where you are attempting to connect the blue wire, it's hard to answer your question about "splicing".  Normally it's easiest just to connect the blue to where the original ignition coil plugged into the harness.

It sounds to me like you might have a filament burned out in the headlight or the wires not connected correctly to the bulb.

I plan on connecting the blue to the black and white wire where the wiring from the key switch joins the main harness.

The headlight works in both bright and dim, I can see it go to single filament when on dim, the bright just doesn't work at the place it is supposed to, you have to push it toward the low beam setting a little, then then both filaments come on the high beam indicator light comes on as well. It's not coming on at the dentent or whatever is in there, you slide up just a hair and it comes on, you let go of the black switch and it will move back down go off.

Low beam is one filament and high beam is the other filament.

When both filaments are on, that's not high beam.  That's the transition in between low and high beam.  Yamaha did this because if there is even a momentary loss of load on the magneto when switching beams, the voltage can spike and blow the bulb on the stock bike.  

I'm not sure how you can tell both filaments are on as they tend to be hard to see and pretty darn bright but I'll take your word for it.

If the high beam indicator is only on in the "mid" position, sounds like you have something going wrong in the switch.

I would imagine that DEET would have a look at it for you.

If doing yourself, the switch type with two thin copper strips/inserts, slightly shaped, are tricky little beggars to fit (some YHA205 switches have one copper piece with two "pimples" above a single "pimple", with the single in permanent contact with the plate attached to the blue wire). You have to pinch the two plates on one side and the ball bearing on the other, with the spring in between - with my big, clumsy digits it can be a pain!

You are right about the headlight, I don't what it does, my headlight is not in the bucket so I looked at it from the side, all I know it is looks different on high and low, the light source seems to change position. I think I have the switch problem figured out, there a contact on the bottom of the black switch button, it touches the contact for the yellow wire and blue wire when in the high beam position, you slide the black switch button to low beam and the contact then touches the blue wire and a green wire. I'm not getting contact with the blue wire when in the high beam position, it is missing good contact by just a hair. It's only missing good contact by about .6 mm or less.