Since I already have the 6 volt H4 coming, and just picked up some silicone O-rings to use to mount it into the reflector, I'm going to give that a shot. I also ordered a universal 6 volt regulator, rather than risk burning out the new bulb. I wasn't previously aware that Yamaha had a TSB recommending a regulator.

www.ebay.com/p/25041393458

The 6 volt H4 will be fine, the beam spread gets a bit crazy, but fine for daylight running, which is what you wanted.

Yes, regulator is a bulb saver.
On my CT1-C I fitted the smaller version under my tank (see thread #80 on the below link) and on my CT1-B I fitted the larger version under the seat near the battery.
I've seen guys here put them under the horn which keeps it cool and easy to connect to the instrument lights blue wire.
www.yamaha-enduros.com/index.php/forums/...restoration?start=70

Thanks for the info Pete. I really like the clean way you mounted that under the tank. I'll do the same, assuming it fits (which I think it will). If not, there's room under the seat. In the eBay ad they said some folks put it inside the HL bucket, but I want some airflow on it. I'm also aware it needs a solid earth connection to the frame.

I received the 25 watt H4 bulb today, and just fitted it into the reflector. As expected, the flange was way too big, so I carefully trimmed it with tin snips. The bulb came with a foam protector that I kept around the glass that helped from hitting the bulb with the snips.

 A problem I didn't anticipate was that there's also a shoulder that is 3 mm too big to go through the reflector opening. So rather than trying to enlarge that opening I put the two O-rings I purchased in, put the flange  on top of those, and that worked well. Put the wavy washer over the flange, then bent the tabs down with a small rubber mallet, with the assembly on a thick folded towel.

The prongs stick out further than the stock bulb, so with the plug on it almost hits the back of the bucket, but it does work.

 I'm going to wait until I get the voltage regulator before I try it. Should be here Friday or Saturday. I've already spliced a wire to the dark blue wires and tested it, and it's the correct wire. Hopefully it's going to fit under the tank like Pete's.

 I also discovered something. Since I've gotten this bike going I've always turned it to the headlight position before starting. It's always taken two kicks with the choke on, but now I've just been turning it to the on position, and it starts with one kick real quick! I guess it's getting more spark without having the head and tail lights on? 

      

Very very interesting things going on & thanks for posting. I'm keen to know how the light pattern ends up as it relies on how far the bulb sits forward in the reflector. In replaceable bulb reflectors like we had in nz we got a pile of cheap bulbs that didn't sit right & had to go through them to get a good one to show a positive pattern for high & low beam otherwise the beam was just everywhere & nowhere--not focused. Very clever what you're doing though.

Here's how the bulb looks inside the reflector. After I get the voltage regulator installed I'll take it for a ride at night and see how it works. I did hook it up directly to the battery on the workbench, just to test it, and the high and low both work. They also seem brighter than the original. According to the seller this 25 watt halogen should not cause any heat damage to the original H4 connector, or wiring.

 

If ya playing with battery powering it you could just pull the bulb back & then push it forward & if poss take out the extra washer & just see how it looks on the wall. Changes a lot if you can get it far enough forward.
That's real trick what you've done. Neat & tidy.

Sorry forget that now the tabs are folded over. Might not be lucky bending them twice.

The problem is I can't push it any further forward, because of the metal bulb shoulder won't go through the opening, and it can't go back either. I did a test with it on the floor in my dark garage, and it's not a great beam. Lot's of dark areas, but it should be fine for daytime running. The metal back of the bulb does get hot, so I'll have to make sure it's not in contact with other wires in the bucket. I can probably make a heat shield for it from aluminum duct tape.

youtube.com/shorts/5SFAjtL8P3M?feature=share