Verify a good ground point for the test light by clipping the test light to the proposed ground and probing a known B+ source in the fuse box. If the test light illuminates, the test light ground is valid.
To verify power to the bulb socket, switch power to the bulb circuit ON and probe the socket terminals. If the test light illuminates, the bulb socket is receiving power. Note that only one socket terminal should illuminate the test light. If both socket terminals illuminate the test light, either the bulb ground is open or power is being delivered to both sides of the bulb socket. To determine which is the case, remove the bulb and probe both socket foils on the PCB. Only one foil should be energized.
To verify ground to the bulb socket, clip the test light to the B+ source used earlier and probe the opposing bulb socket terminal. If the test light illuminates, the bulb ground has been verified and the issue is with the bulb, its socket, or socket connections. If the test light does not illuminate, there is a ground fault.
More than likely the problem is with the new PCB. Are the foil contact points for the sockets and the IP harness connector bare copper, clean and bright? You can use a soft pencil eraser to burnish them if needed, but be careful not to dislodge the foils from the PCB substrate.
1
