Hi all,
Brand new owner of a '75 DT175b.  Picked up the bike, everything worked. Took it home for short ride and when I got back the neutral light stopped working.  First thing I checked was grounding the blue wire from switch onto the engine case, light came on, not a bulb or wire issue. Second thing I checked was taking out the switch with blue wire attached and touching/grounding the contact of the switch to the engine case, light came on.  Reinstalled everything but no neutral light. Yes, I'm sure it's in neutral.  Is there something in the gearing shaft that's missing the switch?  Very confusing as it was working fine before my test run.  Any help is greatly appreciated.
Justin

Ok, you answered my first question. So second one is the button still springloaded in the switch--never seen a faulty one. Are the engine mount bolts all tight--pretty unlikely cause. Look down the hole for the button on the drum but can't see that escaping. Is there a thicker than normal washer under the switch, try it without a washer. Bit of a mystery. Neutral 'is' between first an second you know--Sorry, shut up 'me'. ps, think you said blue so that's a light blue? not the darker blue of mag lighting to instrument illuminating bulbs?. Anyway--was ok & then it wasn't. Tighten that vibrating engine. Think rear top is rubber mounted anyway but!!, rest are solid. Oh, & check loom earth likely at the coil mount under the tank.

Thanks for your reply.  I'm an idiot.  Apparently I wasn't in actual neutral.  I must have been in false neutral as I could push the bike around thinking I was in actual neutral but with no neutral light on.  Did some reading and realized I had to just do a light up tick on  shifter after getting it in 1st.  That put it in real neutral and light came on.  Relieved and embarrassed at the same time.

Hey all good haha. I felt bad even half joking it might not be in neutral.

Very easy thing to do especially if you are knew to riding. Heck I can remember as a kid on my first bike. Even after having the bike for a while I would have the bike in neutral and the light would not be on. All it would take is to hit the shifter a HAIR and the neutral light would come on