Motorcycle Repair: Dim headlight problem, yamaha dt 250, lighting circuit

Question
Hey I was wondering if you could help me figure out a puzzling problem I
have. For starters I have a 1974 Yamaha Dt 250. Fun little bike. All the
electrics work, except the headlight. The headlight works, but is very dim. It's
a 6v 35w sealed beam light. The light that originally came with the bike was
blown and it was a 6v 30w. My light turn on and switches beams pretty
slowly. I tested the wires off the light to see what kinda voltage it was getting.
The meter only showed about 1 volt, but it's possible that the meter is faulty.
The magneto seems to be in good order, and the lighting coil is in good
condition. Also the headlight runs right off the magneto, only works while the
engine is running. Could there just be a bad connection, or bad rectifier.
Sorry for the long e-mail, but I know the info will help diagonse the problem
in some way. Thanks alot! -Matt

Answer
Matt,

1 volt is pretty lame, may be a bad ground.

-have you tried running a ground wire to
the engine from the headlight ground?

-Possibly a problem in the light switch
or ignition switch.

-Does the light work okay if you connect
it to another power source like a battery?

-does the magneto flywheel seem to have
good magnetism?

-check the wires and connectors for corrosion
or shorts. Try some new wires from the lighting
coil output to the headlight.

-the rectifier is likely just on the charging circuit
not in the lighting circuit. Have you tried
disconnecting the rectifier?

-last thing is probably a short in the lighting
coil that reduces the output of the coil.