LED conversion, 1971 Scamp

The only thing that comes to mind as common to both turn signal sides is the turn signal switch in the steering column. Remove both front LED bulbs. Install only 1 normal bulb. Check for voltage at the other socket with a digital VOM. I'm thinking the voltage is there with normal bulbs, but not the current. Since LEDs don't require very much current to light up, that low-current is sufficient to light up the LEDs, but not normal bulbs. The solution would be to find the cross-drain at the column switch (maybe new switch, maybe just clean up the old one???).