I have this cheap copy of a 50s Precision Bass, which came with an ugly pickguard. So I made a new pickguard, and in the process of fitting it to the bass, I scraped off the protection tape on the side of the pickup, and the wires became visible.
When I was done, I noticed that the bass is now picking up hum when I'm not touching the strings, which I'm fairly sure it didn't do before. The hum goes away when I touch the strings, and I can turn it off by turning off the volume pot on the bass. It doesn't seem to be the cable, or the amp - plugging it into my guitar doesn't result in hum.
So I have a couple of related questions:
- What is wrong with the bass? Did I accidentally damage the pickup, or tear off a ground wire? How do I diagnose this?
- What can I do to fix it? A brand replacement pickup would cost roughly as much as the bass...
Edit: As requested, here are some images, and the results of some tests with the multimeter.
As far as I can tell, all points that should be grounded have a good connection (1 Ohm or less) to the outside of the output jack. What worries me is that I cannot measure the resistance of the pickup - from what I understand, there should be some 5-20 kiloohm between the two poles of the pickup, depending on the construction, but my multimeter shows infinite resistance.