Humbuckers or single coils? If you wire humbuckers incorrectly it can make the output quiet. Also, have you set the pickups to be the right distance from the strings?
4 output wires from the pickup? That setup can accidentally be cross-wired so the outputs from the 2 halves of the pickup basically cancel each other out.
Humbuckers or single coils? If you wire humbuckers incorrectly it can make the output quiet. Also, have you set the pickups to be the right distance from the strings?