This is the sort of half-hour project which anyone can make (except of course that one never gets round to it), and which should be part of the standard tool kit of any serviceman, road crew, or retail shop. It will tell you whether a guitar lead is shorted, and whether both leads connect through to the plugs at each end. What is more important is that it will do these tests without the need to hold test leads onto the plugs, so you are free to bend or stretch the guitar lead in case it has an intermittent fault. It is common for a coiled lead to test O.K. when relaxed, and to crackle or cut out, only when stretched to a particular length. The diagram is self explanatory. The battery life should be the "shelf life", and if you use (say) a leakproof L.P.U.ll cell or similar, you can solder it in and forget it.

(It is also generally much easier to solder to the ends of a leakproof cell.) The bulb may also be soldered in, and held behind a hole in the box, with a dab of epoxy. Any old box will do, but if it's metal, be sure that the box does not short out any of the wiring, and pack any loose parts with foam.

Diagram of Guitar Lead Tester:

Plug either end of lead into A and bend/stretch it, particularly near both plugs. If light goes on or flashes, lead is faulty (short-circuit) Now also plug other end into B and bend/stretch cable. If light is not on, or flashes, lead is faulty (broken conductor).