Thanks MarkT for the info.  I'll have to diagnose why my tail light isn't coming on; perhaps that messed up switch or maybe something else (wiring to/from the tail light itself).  I did find Pobit's flasher replacement on eBay....thanks!  Regarding the new switch....it looks like the wire colors match the wiring diagram I have, so maybe it will be a plug & play replacement.  I plan on doing it one wire at a time to be safe.

Some of the colors might match but if the listing is correctly listing the colors, not all of the colors will match.  No light orange/white on your bike for example...  And with aftermarket switches, sometimes the functions are the same but colors are mixed up...  a green on the new switch might be the Yamaha brown for example.  Or maybe they match up really well?

It would be prudent to use an ohmmeter or continuity tester to check what wires you think belong where against the Yamaha light switch map.  It's not hard to do and can save burning stuff up. 

I hear ya' MarkT.  I just went out in the garage to double check the wire colors.  Everything matches (color-wise) with the exception of the "light orange-white".  On my bike, it's actually a light brown-white (to me anyway), but it looks like the same color in the seller's photo.  I also took apart the switch and I see what you mean about the 3 positions of the lights on / lights off switch.  I have continuity from the blue wire in the switch all the way to the blue wire at the tail light, but obviously no light there because of the buggered up switch.  Thinking in terms of today's bikes, why did Yamaha choose to have an on/off switch for the lights anyway?  Did people actually gain some sort of advantage (other than bulb life) by turning the lighting off when riding off-road?

What doesn't make sense is not being able to control the lights.  It's wasn't an advantage to be able to turn the headlight off on an older bike, it was "normal".

I think the date was January 1st 1978 when all new motorcycles sold in the USA were required to have an always on headlight for safety.  It's thought that a headlight in the daytime makes a bike more visible to cars.  But there's still tons of accidents where a car turns in front of a bike.  Curiously enough, I read a study once where wearing a white helmet made drivers notice motorcycles better than anything else. Even bright or dayglo colors weren't as effective. One theory was that cops wear white helmets so that's why people in the study noticed the riders with white helmets more than anything else. 

Well guys, it would appear that I have a MAJOR electrical problem with this bike.  This will be a long post, but in an effort to finally find a solution…I want to be as detailed as possible.=16.0ptI bought this bike 2 weeks ago.  Before I did, I gave it a quick test ride around the subdivision the seller lived in and it ran fine.  I knew at the time that the lights did not work, but I figured I’d have plenty of time to diagnose and repair those issues. I put a brand new Yuasa battery in, took a quick look at the wiring and repaired the most “obvious” faults (disconnected pigtail connectors, etc.)  The day after I bought the bike, I rode it to a gas station in town to fill it up with non-ethanol gas.  That trip was about 10 miles round trip and again…the bike ran fine.  The very next morning I wheeled the bike out to leave for our annual vintage bike ride.  It started fine and about 2 miles down the road it started missing and backfiring wildly.  I pulled over and noticed that the bike would idle pretty well, but the slightest amount of throttle would result in more terrible missing and backfiring.  So, I pushed the bike home (mostly uphill, of course) and knowing I’d never make it to the starting destination of the ride on time on my ’75 Hodaka Road Toad…I went on a “vintage” ride with my 2012 BMW K1600GT.  Embarrassing, to say the least.  Since that day, I’ve been going over the bike with a fine tooth comb…focusing mostly on wiring.  The first major fault I found was in the wiring coming from the stator.  Where that harness plugs into the connector on the right side of the bike, I found that the black and yellow wires had been cut, stripped and then simply twisted back together and covered in electrical tape…with about 50% of the copper strands not even making contact with each other.  I cleaned this mess up (stripped back to good wire, soldered, heat-shrink tubed) hoping that it may have been the source of the terrible running engine AND the lighting problems.  After that, I cleaned every ground I could find and suddenly I had all 4 turn signals, the brake light and the horn working (off the battery only….I still had not started the bike) perfectly. Thanks to advice from MarkT, this morning I was even able to fix the broken “lights on/lights off” slide switch and now have the tail light working as well!  I had already wired in a voltage regulator and put a new rectifier in as well.  As far as non-electrical things, I checked for good fuel flow from the petcock and took apart the carb only to find it virtually immaculate in terms of how clean it was.  So, this afternoon was to be the moment of truth.  I started the bike and… it ran like crap.  The idle was about the same as it was the day I had to push it home, and again…applying more throttle made it miss and backfire like crazy.  But that’s not all.  When the bike was running, NONE OF THE LIGHTING WORKED AT ALL. I was stunned.  I feared I had somehow just blown all the bulbs.  I turned the key off to stop the bike and then turned it back on to check the turn signals, horn, brake light, etc. but NONE of them worked!  At this point I began checking grounds again, checked the fuse….all was good.  I walked away to clear my head and came back for another look about 20 minutes later.  I turned on the key and you guessed it…all the lights worked again.  I sat there in disbelief, but happy that I hadn’t blown any bulbs.  The only thing I will add to this story (I forgot this had happened) is that last night something very similar happened when I went out to look at the lights/turn signals switch that MarkT was helping me with.  I had also been working on removing the flywheel yesterday and had taken a break for dinner.  When I went back out to resume working on the tail light issue, I turned on the key and had NO lighting!  Being as baffled as I was today, I was about to give up on it when I wondered if by turning the flywheel earlier I had disturbed something stator related.  I gave the flywheel about 30 degrees of counter clockwise rotation and suddenly (I had the key still on and the left turn signal on) I had lights again!  I really have no idea how this part of the system works, but I guess I just assumed that perhaps the points needed to be closed to complete some sort of circuit with the bike off?  Probably way off base here, but I don’t understand how turning the flywheel could cause the battery-fed lights to either work or not work.  Something is definitely messed up here, and I’m wondering if a stator rebuild by DEET should be my next move.  I’m planning on checking to see if my timing is set correctly tomorrow (I bought a dial gauge and made a little “test light” with alligator clips) and watched some videos that other forum users here have linked to, so it seems pretty straight forward.  Is there anything here that jumps out as something I need to check or test first?  Condenser?  The obvious scuff marks on the source coil (I assume someone used a claw-type puller on the flywheel)?  Ignition coil?  Any help or suggestions are greatly appreciated. 

Check the rectifier under the tank.

That lighting coil looks bad too. 

MarkT, I did in fact replace the rectifier with a brand new one this morning, even though from what I could tell...the old one tested fine.  I guess I have my two coils confused...can I assume that the lighting coil is the one on the right?  The thing is, would either the rectifier or the lighting coil cause the engine to run like crap and backfire?

Probably wouldn't make it run crappy.  But rectifier could allow battery to discharge through stator.  Make sure you have it installed in the correct direction.  White goes to terminal with the ~

First thing I would do is center the stator in the slots and set the timing.  Then see if max point gap is in spec. If it is great, if not, replace points..

If that doesn't fix the running, I'd change the condenser.



 

Yep...that's exactly how the rectifier is installed, MarkT.  I'll center the stator, set timing and check the point gap tomorrow and see what happens.  In terms of replacing the condenser....two questions:
1.  What exactly does the condenser do and what usually happens when you have a bad one?
2.  I've heard that it can be somewhat difficult to solder all the wires to the condenser.  I seem to remember reading about an option to mount & wire it into the system somewhere other than on the stator.  Is that a good or better idea?
Finally....doesn't it seem really odd that all my lighting now works fine with the engine off, but as soon as the engine is started, it all cuts out?  Have you ever heard of anything like that before?
Oh....I contacted DEET and he responded right away, but told me he has such a backlog of work right now that he wouldn't be able to help.  Any suggestions for any other person or company who does the complete stator rebuilds?
As always, thanks MarkT.  I really do appreciate your help.

Replace the lighting coil. It is destroyed.
That is more than likely the root cause of your problems.