Need a meter to check for continuity. The free ones from Horrible Freight work fine for this, sometimes they are given away if you buy enough other stuff, otherwise it's maybe ten bucks.
You want to set it on "ohms" which is kind of an upside-down horseshoe shaped symbol (greek letter Omega). Set it to the lowest level. Maybe 200 or so. The display should read '1'. Now touch the tips of the probes together, the display should go to 0 or close to it. .Now, when you touch it to either end of a wire, it should go to 0 or close to that. A ground wire should show 0 or close to it, if you touch one end of the ground wire, and the other to a bare spot on the body or frame.
If it doesn't go to 0 when you touch each end of the wire, then that part of the wire is broken inside the insulation. Anyway - figure out where the wire STARTS and where it ENDS and start testing till you find the break. The speaker works, so you have a wire problem, most likely.......