Is there a way to test my printed circuit in my tail light?

If none of the lights work on either side, you have a bad ground. Since you know how to test for voltage TO the lights, measure on the other side of a bulb when that circuit is turned on and you'll see some voltage there too. Follow the copper circuits and wires until you find the spot where there is no voltage. That will identify the location of the break.

If the bulbs are dead on only the left side but the signal light appears to work when no other lights are on, remove the bulbs from the right side and you'll see the left one quit. That's proof of a bad ground.