I did a swap of a pair of Bart BH2s from an Ibanez EHB for a pair of Bart MK5CBCs, which had been permanently wired as parallel. I thought I'd make them switchable so got some 4-core cable and re-rewired them, drilled holes for and connected up the toggle switches, got silence, realised I hadn't connected the pickups on the ground side, sorted that out, and now I have proper sound. Woo hoo.