[ray_mcavoy]

There were a couple years (62 & 63 I think) where the Chevy trucks used a single turn signal indicator for both sides. On those, they simply wired the indicator light between the left & right front turn signal wires. They used the front turn signals so it's not affected by the brake lights.

They didn't use any diodes or anything to prevent one side from "backfeeding" into the other. Instead, this configuration simply takes advantage of the wattage difference between the little in-dash indicator bulb and the larger external turn signal bulbs.

One side of the in-dash indicator bulb receives power from the turn signal on the activated side. The other side of the in-dash indicator bulb is connected to ground through the filament of the external bulb on the non-activated side. Since the small low-wattage indicator bulb only draws a tiny amount of current, it's not enough to make the filament of the larger external bulb glow. So I guess you could say, there is some "backfeeding" going on with this arrangement but it's limited by the high resistance of the little indicator bulb so there isn't enough current flowing to light up the external bulbs on the non-active side.