6-volt turn signal bulb 1972 Yamaha LT2 100

There should two separate bulbs for marker and blinker. It sounds like a bulb is burnt out, bad ground, melted socket or a wiring anomaly. Are you certain it's supposed to have 57 series dual element bulbs for blinker and markers?

P/V=A

The panel is rated 6 watts at 12 volts 12 / 6 = 0.5 Amps

So in full sun the panel "should" produce 1/2 Amp at 12 Volts.

What type of 12V bulb and what is its current rating?

i don't know. blinker slows to normal when both bulbs work. using volt meter or similar, test rear socket for a
continuity to ground. if OK test socket for 12 volts from
socket to ground. if OK, bulb is not making contact. if not
OK, note wire colour and look for damaged or loose
connection from front. check white back up light as well.

Instead of being a H-D ick like you know who I would suggest that you start by checking your bulbs for resistance. Sometimes they look okay but the thin filament inside may be broken. If the front turn signals work, then your rear signals should work, so your push button and Flasher is okay. Check the wiring at the bulbs for voltage. Test the bulbs as you depress the turn signal button. Use the metal of the bulbs base for ground and check the other wire for voltage, if there is no voltage, you may have a bad ground at the base so attach the ground to the batteries ground. Still no voltage? Most likely there is an issue with the wiring towards the rear where the harness connects the positive line from the Flasher. If there is some voltage at the bulbs (assuming your battery is fully charged) then be sure to check for corrosion on the inside of the turn signals base and also where the ground wire terminates at the frame. Next, locate the wiring harness lighting circuit for voltage. There may be a break in the line leading to the bulb. There are 12 volt 'wiggies' that will help you locate a break in an electrical line.

I assume you must have also checked the rear turn signal bulbs.
You may have to start using a volt meter. Check for 12 v at the bulbs also check the bulb ground...that's a common cause of light problems.

they run on a 6 volt system

What you speak of as to the left blinker doesn't flash, yet the instrument cluster shows the green arrow (to the left), and yet that and the left turn signal lights do not flash, appears to be a simple burned out bulb. If one of your left turn signal bulbs are burnt out, then the #552 Flasher Unit in your fuse box is NOT the cause. It's the "Amperage" not being correct to the flasher unit. Place the parking brake on and start your vehicle. Put the left turn signal on and check to see ALL the bulbs are illuminated for the left turn signal. If you find one bulb that is not illuminated, then replace the bulb. It should be an 1157 bulb, but in the front it could be a 1157 Amber bulb dependent on whether your turn signal lens is clear or yellow.

If you still have difficulty finding the dead bulb, turn on the right turn signal and see which bulbs are illuminated and this will give you an idea as to which bulb on the left side isn't working, or turn on your Emergency Flashers which will turn on both the left and right side lamps and see which bulb is not lit up.

I hope this Helps,

~00 Buck~

"Still living on the Right Side of Dirt..."

Its a big job unless you can find a similar model that is 12v and you can swap some parts.
The stator\lighting coils would need to be rewound,and you will need a new ignition coil and regulator plus all the bulbs and battery( which may not fit in the 6v holder) I was only 2 in 1962 so I cant remember if it has a starter, if so it would be virtually impossible to change the starter from 6-12 without basicly remanufacturing it.

check for ground remove one of the rear bulbs and with a 12 volt test ligh see if you getting power to the socket if you are then you might have lost the body ground