Can't seem to track down why my headlight and gauge lights won't turn on.1975 Yamaha DT175 with a Vape 12V system, l've upgraded all the bulbs to 12v, including the headlight, and they're all new bulbs and I've tested them and they work.Anyone know why they might not come on? I've got a good battery, when I run the bike they don't come on either. Any ideas?

Someone didn't connect the headlight circuit when the VAPE was installed.  It's a modern Permanent Magnet Alternator (PMA) system with extra power and a robust electronic voltage regulator/rectifier.

The original Yamaha PMA system had to be carefully designed to have the output match the load to regulate the system voltage...  the electronics back then were not nearly as advanced or robust...  so there were parallel power systems to make electricity that were engaged as needed depending on load.  Headlight and gauge lights ran off AC power directly from the engine....  the coil in the PMA for the headlight circuit was designed to put out roughly the same wattage (power) as the bulb load to keep the voltage in the acceptable range.  The headlight circuit coil was only connected when the headlight was switched on.

Your VAPE was designed to put out a generous excess of power and uses electronics to dissipate any excess power to keep the voltage in the acceptable range.  There is just one power output system which is now not connected to the headlight circuit.

Which is all just a long way of saying your VAPE isn't wired correctly. 

I knew you’d have an answer! So here’s the thing, after digging through what I’ve got, I’ve realized that the Hi/low switch assembly wasn’t the correct year for mine and it’s not entirely correct so I’m gonna either get a correct one or try to troubleshoot which wires go where. My question is, for you mark, given that new information, is it possible I have the vape system wired correctly and just the switch is wired wrong? Would that make the headlight not burn? I’m curious, as it didn’t really say, whether or not the headlight and gauge lights be *on* when key on, engine off, with the new vape system. Or does the system still require the bike to be on for the gauge and headlights to run.

Lastly, my other issue is the vape system didn’t seem to have a neutral switch wire, how would I go about wiring that to show in the cluster?

I wish there was a simple answer.  And there could be.  I just don't know how you wired it or what you have as far as a headlight switch. 

Also, how do you want the headlight to work?  With the VAPE, you can have it run off the battery and on your model (Headlight on-off switch is in the handlebar switch) headlight would even work with key off. 

You could also wire it so key must be on for headlight switch to work.

Or you could wire it so engine has to be running for headlight to come on. 

As far as the neutral light...  there is a very light blue wire (sky blue) in the harness the original ignition plugged into.  It's often faded and discolored so hard to tell the color sometimes.  Anyway, when that wire is grounded with key on, the neutral light comes on.  You just need to run a short wire from neutral switch to that wire. 

Thanks for the responses Mark! You to me are the premier source of info

Ideally I'd like it to run when the lights come on, so like, when I put the handlebar switch "lights" to "on" (tail light on) ideally the headlight and gauge lights come on, which I would imagine would be off the battery, and when the bike runs it would charge the battery. Any idea on how I would achieve that outcome? Assuming the handlebar switch is correctly wired. 

As for the neutral light, I just need to isolate that sky blue wire from the original harness in the headlight bucket, and that's the neutral wire? I noticed in the hi low switch wires there's a sky blue as well. I'm guessing that wire somehow lights up the blue neutral light in the gauge cluster? I guess i'm confused as to how I can get that wire to run, from the neutral switch itself to some other wire to make it active. Sorry if I'm not grasping, I'm still learning lol.

"....As for the neutral light, I just need to isolate that sky blue wire from the original harness in the headlight bucket, and that's the neutral wire? I noticed in the hi low switch wires there's a sky blue as well. I'm guessing that wire somehow lights up the blue neutral light in the gauge cluster? I guess i'm confused as to how I can get that wire to run, from the neutral switch itself to some other wire to make it active. Sorry if I'm not grasping, I'm still learning lol. "

NO!  That's not what I said at all.  When did I mention a "sky blue"  in the hi-low switch wires or mention the headlight bucket?  You're probably looking at a plain blue wire and not the very light sky blue?  I don't know.  I very specifically mentioned the connector the original ignition plugged into.  That's in the middle of the bike.  Nowhere near the headlight bucket or switch. 

You might just be learning and that's great.  Taking information and going off on your own to find your own solution is fine too.  Just make sure you fully understand the information or be prepared to blow fuses or melt wires.  The harness the original ignition plugged into should have about 5 wires from memory.  Black/white (sometimes solid black), Yellow, Two Greens (one or both of which have stripes), and the Sky Blue (which often looks dirty white, maybe with a greenish tinge.)  This connector is probably about 6 inches from the neutral switch. 

You're free to find some wires in the headlight bucket you're guessing are the same and string several feet of wire to connect them to the neutral switch.  Seems easier to me to do it my way but it's your bike.  (Hint: If you want to make a connection in the headlight bucket, look at the wires right at the neutral bulb holder in the gauge.  One wire will be brown (power) and the other will be the very light Sky Blue)

If you want more help, you'll need to take photos and use a third party hosting service to link or post them here as site photo hosting is down right now.  I'm not going to try to do this blind. 

I'll keep my head down--too much for me this modern stuff. But where your sky blue goes to the bulb there should be a DC brown [light brown] feeding the bulb on any yamaha .
Talking browns--Dark brown just to confuse is blinkers one side & dark green is other side.

“As far as the neutral light...  there is a very light blue wire (sky blue) in the harness the original ignition plugged into.  It's often faded and discolored so hard to tell the color sometimes.  Anyway, when that wire is grounded with key on, the neutral light comes on.  You just need to run a short wire from neutral switch to that wire. ” 

Sorry I confused myself earlier and should have really read this again while looking at the bike! Thank you for the help, I’ll work on my listening skills in the meantime as well! Your method sounds much easier and I’ll look into it tomorrow  

Found the sky blue wire you’re talking about! Underneath the oil tank in a connector. I’ll hook that up to the neutral switch via a wire and then it should be good? 

As for wiring the headlight to run with lights on now… hmmm. Any ideas? 

I think you need to post pictures as MarkT asked for google photos Imgur or Dropbox he’s driving blind just my .02 worth