Another stupid newbie question - hummmm

[Lefty W.]

So my Mission amp kit is finished and it sounds great - as long as I'm touching the guitar strings. Almost no noise. When I take my hands completely off of the guitar, there's a loud buzz or hum. The guitar is a dual humbucker Explorer copy of some sort that was "rescued" from a dumpster. I rebuilt it from the husk up. It is entirely possible that I re-wired the guitar incorrectly.

Am I correct in presuming this is a grounding issue with the guitar, and not in the amp? (Also presuming I haven't yet used up my stupid newbie question quota).

[MWJB]

If the amp doesn't hum, with no guitar plugged in, it's the guitar that is the problem.

[Tom Phillips]

I had the same problem once. Turned out that the ground to the bridge and strings in the guitar was bad.

[Lefty W.]

If the amp doesn't hum, with no guitar plugged in, it's the guitar that is the problem.

I'll try that tonight. I'm also suspecting the discount cable...