First of all, I know nothing about guitars. However I did build a distortion stomp box for my nephew, who plays a 1974 Gibson Marauder with 2 double coil humbucking pickups side by side near the neck, and one single coil pickup by the bridge.

The distortion box worked fine with a line level signal going in, and the output to a 'scope. But there is no sound when the guitar is connected to the box, and then to an amp. (it's fine on bypass, though)

I haven't had a chance to look at the box yet, but I am wondering:

Does the output from the guitar need to be pre-amplified before it goes into the stompbox? What is the voltage level output of the humbucking coil pickup?

Thanks,
Santa

This has nothing to do with it. You might a have a cold solder joint in the circuit somewhere. When you plug it in it should work fine. When the batterys dead it does the same thing.

I believe Gibson humbuckers have an output of around 9k-14k ohms. Some may be less and others more.