Ok i'll guess untill pics are sorted but don't dwell on my guess.
White makes me think rectifier & black is earth unless it's the magneto ignition wire from points etc.
So thinking it's likely earth, joining it to white wouldn't end well.
Don't overthink that thought--but!!.
ps, i just use google photos,-- not sure why,-- then link the pic which is only a link to click but better than nothing. Obviously not as good as Imgur by the looks.

White is likely the "booster" for the charging and is usually not connected.

If the black is a single female about half way up the wiring coming from the magneto/flywheel, then this too should be left alone - it is to do with setting the points or timing and the engine won't run if it is connected to earth (the other black wires).