I have a 2003 Epi Les Paul Black Beauty, which I had modded with a Seymour Duncan '59 in the bridge slot and a Duncan SH-4 JB in the neck position.
However, I have always encountered an issue with both of the volume pots on the LP in that the volume of each pickup - regardless of the bridge or neck being selected individually on the 3-way toggle - does not gradually increase or lower as I turn the volume knob. Instead, it seems that the pickup selected is either "on" or "off", on full volume or turned all the way down.
Despite having had a US-made wiring loom installed, which featured CTS Bumblebee caps etc. in order to emulate the classic '59 Gibby LP setup, this problem has persisted. It is doing my nut in, especially as I require to turn the volume either up or down when playing quieter passages on ballads etc.
When I am playing the guitar, I can't find any difference at all, regardless of how much or little I have opened the volume up. It seems to be acting as simply an on/off for the respective pickups(s). I'm thinking of uploading a photo of the innards so that any interested parties could have a gander at it and give me their opinion.
Another thing that puzzles me is that when the guitar was being worked on in the stores I took the BB to in order to have the mods carried out, the guys in the stores who operated(;p) and then tested the guitar didn't report any problems whatsoever - all I got from them was "it has a nice sound", and "believe me, you'll definitely notice the difference".