Confused on Lawrence 710 wiring and 'hum'

[Joe Alterio]

I've been noticing that when my guitar (Zum) is plugged in and I am not touching it, there has been some single-coil-type hum. The hum worsens if my finger touches the aluminum neck....but the hum softens when I touch any other metal part of the guitar.

I checked my wiring on the pickups and freshened the soldering...but I noted there is a red wire coming from the pickup that was cut off and not touching anything. Well...when I would touch it to something metal like the changer, almost all hum goes away. But everything I read online about this red wire says it should just be chopped off unless you need it for a switch (coil tap?)....but perhaps that isn't correct and this is working as some sort of ground?

I secured the red wire to a screw under the changer and now the hum is mostly gone, and when my finger touches the neck it doesn't make a change to the hum level (e.g. no longer gets louder).

I'm not good with electronics - am I killing some of the frequency range of the pickup by doing this...? Is some level of hum normal and I should leave the red wire unsecured from the guitar?

[Bruce Derr]

The red wire is the connection between the two coils in the pickup. I just verified this with an ohmmeter on a loose 710 pickup I have. As you said, normally the red wire would be left disconnected, or it can optionally be connected to ground through a switch, which lets you short out one of the coils to make the pickup a single-coil, rather than a humbucker. The tone of a humbucker pickup in single-coil mode is typically brighter with slightly less volume.

Normally I would suppose that a screw under the changer would be electrically connected to ground (the sleeve connection of the output jack), and that connecting the red wire to that screw would therefore short one of the pickup's coils to ground. However, you didn't mention any change in the pickup's tone (other than the noise level), which makes me wonder if perhaps the screw, and the changer itself, is not connected to ground on this guitar. (That also might explain the noise.)

Try this:
1. Remove the red wire from the changer screw. Leave it disconnected (tape the end).
2. Connect a new piece of hookup wire from the screw under the changer to the ground terminal of the output jack.