I am helping my son get a '77 KZ650C1 on the road. Has been sitting for a looong time. We have gone through the carbs and gas tank of course...yada yada. The 70's bikes had a marginal charging system at best for the most part. I did some calculations as to how much current the incandescent bulbs drew. Then I calculated what the led replacements would pull. The incandescents would pull 13 amps. The leds will pull 3 amps. I ordered led replacements and started putting them in.
With only incandescents when I started the bike a volt meter read approximately 12.3 volts at an idle. Just enough to barely keep it running for long idle times. I replaced the tailight, turn signal front and rear. The idling voltage went up to 12.85 volts. I am sure that when I replace the instrument cluster and indicators with leds the bike should be at LEAST lightly charging the battery at an idle.
In most cases when you replace the 1157 1156 (turn signals) you have to replace the turn signal relay with a tansistorized version. I will handle led or incandescents and flash at the normal rate.