MIMF

I am building a three string resonator guitar and installing one of Nationals single coil mandolin pickups in the cover plate. (Similar the their hot plate design) I am using a wiring diagram for one pickup with a volume and tone pot that I found on Seymour Duncan's sight. I wired everything up as it showed on the diagram and had a ground buzz.... I went over to a friends that has built a number of electrics, he checked everything against the diagram and re-soldered my connections. Used a meter found there was continuity... the buzz persisted! We then replaced everything with the exception of the pickup and the buzz continues. Does anyone have and suggestions on what I should do at this point? If there is any other information I can provide please let me know. Thank you in advance for your help

1) Does it happen with a different cable?
2) Does it happen with a different amp?
3) Does it happen if the wires to the PU are reversed?
4) Touch one meter probe to a wire, the other to each of the magnets. Is there continuity?

Try 'em all.

Ahh... I had a similar issue with Resonator builds and Magnetic pups.
I'll be willing to bet you need a 2nd Bridge ground to the Resonator cone. If your pickup is mounted in the cover plate then it is sitting over your metal Resonator cone, and like ungrounded strings it will create a feedback hummm.

Just solder a ground lead to the rim of your resonator cone and the bridge ground.

I typically run my bridge ground to my tailblock where it contacts the strings, and a second bridge ground to the resonator cone, since the actual "bridge" is sitting on the biscuit.

Ding Ding Ding no more calls please we have a winner....THANKS.... G.S. Monroe you are spot on. ground the cone and the problem is resolved.... Brilliant!!!