Hi, anyone know what is that part and how should that be wired?  The bike work well enough like that but I'm trying to do a as nice kind of job of what was a mess of a bike all those loose wires are annoying me.  I've read quite a few service manuals even on nearby models and different years plus parts list and could find anything about that one. I've found a service bulletin the lighting voltage regulator and that's about it.  I really can't see the need to make the neutral switch goes trough that thing.  I've been fixing that bike for about a year adding missing parts and replacing a few broken things.   The motor serial match the frame and carb model also. Footrest are probably from a dt50, it had a huge plastic tank from some other bike that was resting on the muffler and prevented for fully turning I found a nice stainless one from an earlier Yamaha model, piston, rings, throttle cable, speedo cable, added a main switch...  I'm mostly only missing a chain guard and than annoying thing, a carb cleaning and fine tuning, muffler is a little loud, the rear plug is missing, I will probably make an extension under to lengthen it a bit and make it oval sized pointing downward.  Then if I enjoy riding it new shocks and a paint job next winter. 

Greetings from Tennessee  

What's your engine and frame numbers? Pretty sure that's not a 1977 model and it's a CDI box? Probably an early 1980's model?

Its 1T9-106xxx, you are right, I did not not notice the way too high number, the 1T9 and lack of references got me fooled but a careful investigation led me to the conclusion it is most likely a 82 dt100j. Now i gotta find a service manual or the wiring schematic for that and that should ease my pain.  edit: by the way is there a way to tell that stupid forum not to resize and turn my pictures for no reason they were small enough already and on the right side...
   

Yep that's cdi wire colors White/red. Brown. Orange etc. But--the unexplained item i'll guess at it being some magic ignition iterupter like PW50's have where you start it & it's limited to about 1000rpm or less then click a throttle switch & away ya go. So does yours have an extra ignition switch click or a magic slide switch on the throttle. Unlikely i know, but can't think of anything else. Also can't think why anything with a manual clutch would need one.

I might have to revise my answer above. Does it have a sidestand switch. Likely related to that so you can't drive off with the stand down. #26.

www.partzilla.com/catalog/yamaha/motorcy.../electrical-1-dt100j

Got that switch, fixed reversed side and wire clipped short but its there alright, I guess a previous owner had trouble with it.