Ac lights to dc lights...is that simple?

Hi all

I have a charging issue but i think i have been looking at it backwards....

I have...
Changed stator..single phase
New R/R
New battery..currently reading 12.25v
Checked all wiring and connections

Bike does this...
With headlight switch connected, charging system only works when lights are switched ON manually but revs drop and sounds underload. Voltage reading on the white wire at R/R is app 5v and the yellow/red wite(lights) is 4v.

If i....disconnect the light switch, bike sounds sweet and the battery charges lovely.

Can i change headlights to dc direct off battery going throu fuse and switch.
Could i use original swith and cut ac supply cable and re connect that to white wire so both recharge battery going throu reg.....phew im confused now.
The bike is a 1998 yamaha neos yn50

Thanks

 

Better to keep threads on the same bike/same problem together, people get lost.