I've never done any electrical work on my guitars, aside from replacing my Strat's single coils years ago and all I had to do was copy what was already done.
My JEM's 5-way and volume pot completely shit out a couple weeks ago. Not sure how, but something with the 5-way cut the output entirely, unless I pushed on it really hard, but then it'd just stop working once I took my hand off. Regardless, it's a 17 year old guitar, it was due time. Add to that, my middle pickup NEVER worked on it's own, from the factory, the connections were fine, so it was probably something to do with the switch.
Being the impatient shithead I am, I went to GC and bought a new volume pot and 5-way. The pot's a standard sized one, so that didn't work out too well. It's on there, but it's at an angle because I didn't want to drill through the pickguard hole to accommodate the size.
Found a wiring diagram and managed to get it all wired up. Before I put strings on, I plugged it and tapped the pickups, they had sound so I put the strings on and started tuning....start playing a bit and think, "Man, this sounds fuckin' weird...."....
Wired the fucking 5-way backwards so my bridge pickup is activated when the selector is in the neck spot. I'm just going to deal with it for now until next time I change strings, then I'll fix it.
I'm going to add a push/pull at some point because I want to be able to use both the inner coils of my neck/bridge pick-ups, (JPM style), I think I'll just bring it to a tech.
I'm not sure if this makes a difference with passive pickups, but I know that it's a really big deal with active pickups. The value of the pots makes a big huge difference, and will greatly affect the tone of the guitar.