You know, one approach when a new problem crops up shortly after some maintenance work (like adding screws to the underbelly) is to put that recent maintenance into the troubleshooting possibilities equation and wonder if something I did caused the new problem. I KNOW this is now 20-20 hindsight, but something to think about when we try to fix things.
Glad you got an answer!!! At least you weren't fighting an intermittent short - one of those on the 12 volt circuit running my refrig took me a long time to find. I kept a lot of fuses around, too.
I seem to remember a technique for troubleshooting a continuously blown overcurrent device by inserting an appropriate voltage small light bulb in place of the fuse. As long as the short is present it provides a ground for the light bulb, and the bulb resistance safely limits the current through the wires. The glowing light tells you that the short is still present. When you remove the short, the light goes out, and it is OK to put the fuse back in. You can also cut and reconnect the wire in question at different places along its length to determine the exact location of the short - cut the wire before the short with the light in place of the fuse, the light goes out; Cut the wire after the short, and the light stays on.
