My CT-1 has been running great, and I've been taking it for some long rides up and down the coast. However today as I was getting close to home, I noticed the turn signals weren't working, and the neutral light wasn't working. in fact none of the lights were working.

 Got home and checked the voltage on the battery and it was 2.7 volts. The battery is only a few months old, and I checked the electrolyte level a month or so ago. So I filled it back up and put it on charge, and checked the fuse and it was okay. After a couple hours when it was back up to 6.6 volts, I put it back in the bike to see if the lights worked. Everything worked, except the low beam headlight filament was burned  out. I put it on high beam and went for a ride. By the time I got home the high beam was burned out. All the other lights still work.

 I checked the rectifier with an ohm meter, and it reads within spec, except that the red wire bullet connector was not solidly connected. In working on it recently, I may have pulled on the loom and pulled it out a little bit. So I'm thinking that might be the issue. However now I'm wondering how the heck do I replace this sealed beam headlight bulb? Does anyone have any hints? I haven't tried to remove anything, there's a collar that looks like it unscrews, but it's tight. Thanks in advance if anyone knows.

I don’t know where it’s posted… but I was carefull and removed the actual bulb and put in a h4(?) in its place… I thought Gr8uncle also had a similar situation…
Voltage regulator in the loom too?
Sneezles61

Yes unscrew the chrome bezel also Napa 4020 seal beam is a replacement bulb

Well there you go.. another solution.
Sneezles61

Thank you guys for the replies. I read some old threads and already got the small bulb removed from the reflector. So the H4 will fit in the opening? Also, is the headlight getting 6 volts AC, or DC? If AC, will these bulbs, including the Napa 4020 operate on AC?

I put a voltmeter in the HL plug with the bike running. Idling it's around 6 volts, but when revving, up to 16+ volts. Is that normal? The regulator seems to test okay using the diode setting on my DMM.

I don't ride at night, so just need it for daytime (the law here).

Amazon has the Hella H4, in various wattages:

www.amazon.com/HELLA-H4-100-80W-Wattage/dp/B000COBLKW?th=1

BTW, would LED work?

www.amazon.com/Motorcycle-Headlight-Degr...730151_t3_B00IKLLJTW

Those are 12 volt, this one is 6 volt

www.amazon.com/LIGHTING-Halogen-Headligh...adlamp/dp/B00GFCB44S

It's also helpful to know your rights and the law.

California law only requires daytime headlight use on a motorcycle manufactured and first registered on or after January 1st, 1978. 

In other words, riding with the headlight off during the day (as defined by law as 30 min after sunrise and 30 min before sunset) and in good weather (visibility over 1000ft) on an older bike is perfectly okay in California. 

Might not be okay to ride and older bike in daytime with headlight off in all states..  but is okay in most states. 

Just like turn signals are not required on motorcycles manufactured on or before Jan 1st, 1973 in the USA.  (Could be an exception in some states if earlier year and originally equipped with turn signals from factory)

P.S.  I believe the law in California says all lights that are present must work...  so if you have headlight installed it needs to work if inspected.  Just doesn't need to be on during daylight on a 1977 or older bike. 

That's good info Mark, and yes I was aware that I don't actually have to have the headlight on with a 1971 Yamaha, but I prefer to. I never did back in the day, but I do think it does make you more visible. Also many young cops may not know the difference, and if I have a headlight on there's less reasons to be pulled over.

I ordered this bulb, and the supplier is actually not far away from me, so it should be here Tuesday or Wednesday. It's 6 volts and 25 W, like the original. I read some reviews on LED bulbs, and a lot of people said they fell apart very quickly from the vibration.

www.amazon.com/gp/aw/d/B00MS98YEU/ref=ya_aw_od_pi?ie=UTF8&psc=1

Is your (6v?) voltage regulator wired into the blue wires in the headlight bucket? It should be.

It might not matter to you, but you'll likely find the clock illumination bulbs are blown as well.

See my post #4 on the attached thread - this shows how I fitted the H4 bulb.

My first attempt at repairing a sealed beam headlight. - Vintage Enduro Discussions (yamaha-enduros.com)

As far as I know I only have the rectifier, not a voltage regulator. I was under the impression that the voltage is sort of buffered by the battery, but because I had almost boiled my battery dry I think that's why the filaments burned out. The instrument back lights are burned out, but that's not a concern. At the very most I would only be riding at dusk, not during the night.

I destroyed the rubber washer removing the old bulb, not thinking I would ever be reusing it again. If this H4 bulb I ordered can fit into that recess, I can either make some silicone washers, or see if any are available locally. I have some thick silicone gloves I could cut them from, using the wavy washer as a guide, or I could even make some from high temp Orange Permatex.

Because when I tested the voltage it went up over 16 V revving, my original thought was to get a 12 volt H4 bulb, which would be dim at idle, but should be able to handle 16 volts. Or should I get a regulator? Or when the bulb is plugged in, with a good battery, will the voltage read differently?

When new, the electrics did work in the way that you suggested. However, Yamaha soon realised the shortfalls of this system and published a Service Bulletin to dealers, advising that voltage regulators should be retro fitted - see link below.

Some members have had success with fitting a 12v bulb.

Vintage Yamaha Enduro Fans - Service Bulletin #M5-084 re Voltage Regulators (yamaha-enduros.com)