Thanks Bill, I just saw you posted as I was replying to the others.
Well, the TM is new to me and I'm only just getting used to it, but from what I've seen, when I looked in the rear compartment there was the fuse holder tied into the red cable which was situated between the two batteries (I'll have to double-check the wiring according to the diagram you posted) and it was toast. What I do remember is that the batteries are two Trojan 105's 6v, if I'm not mistaken and the terminals don't look corroded or anything, they still have those little felt things on them and they look clean. I'll take a picture of the setup when I get home this afternoon.
Well, it does seem like the general consensus is that the speakers and lights aren't connected and that's just a coincidence they're both acting up. My background is in molecular biology, so I'm not really electrically-inclined, feel free to suspect any of my assumptions!
Also, it sounds like I need to just go ahead and buy a volt meter to get to the bottom of this. Are there any features I should look for in one or will any garden-variety meter from Home Depot do?
-Dan