post. You must have gotten to it just prior but now that you mention the larger/smaller wires in the mix it could very well be what happened. If you have a device that requires a minimum, say, number 8 or number 10 wire and you loose that ground (for any reason, loose connection or cut wire) the power is still going to that device. It "Will" try and find another path back to the battery. If it happens to be a small wire then your in trouble. Yes, I fuse everything. On both of my Balmar electronic regulators I have installed a fuse block that has 4 positions. All 4 wires go through that block. Here's what happened to me. I bought a 120 amp alternator and installed it on my engine along with the 80 amp. The original alternator was case grounded and didn't require a separate ground wire. The new alternator required that I upgrade my positive cable but the manual made no mention of installing a separate ground nor did it mention anything regarding a wire size for any separate ground. I thought this was strange because I was starting to push some serious amps. I called the manufacture and was connected with the engineering department because the service department was in the process of moving to another building. I told the engineer about my installation and asked him about not mentioning the ground. I was told that it was also case grounded and I didn't need to worry about it. It worked for two years. It worked for two years because my batteries never got down low enough to cause the alternator to push more the about 60 amps. My solar panels and wind generator and AC generator had always kept up with my discharge. One year after we had returned from Mexico for the summer we were anchored in a little cove close to Mission Bay north of San Diego. We were having camp fires on the beach every night with friends and we hadn't ran the generator for a couple of days. It had been overcast and my batteries had dropped to about 50% capacity by that time. I needed a shower so I fired up the generator because the hot water loop is on the generator and not the main engine. That started the AC battery charger to start pumping only about 60 amps. I also started up the main engine because I knew the AGM's could accept much more then that and I wanted to shorten the charge time. That kicked in the 120 amp alternator in full as well. The regulators were suppose to regulate to what ever the batteries needed so I got ready for my shower. The AC coil and the hot water loop really heats the water fast so it's just a few minutes for hot water. About 5 minutes after I started the main engine I started seeing the smoke. It was coming out of everywhere. I quickly shut down the main engine and then the generator. After I had figured out that we didn't have flames I aired out the boat and went to bed. The next morning I discovered that the ground wire for the regulator had become the ground wire for the alternator and of course couldn't carry the load and acted like a #10 wire fuse. It was bundled with several instrument wires which took the hit as well and I spent the day replacing 5 or six wires. I called the alternator service guys and told them what happened and was told that "of course it needs a ground! You mean to tell me that it's not in the manual!?" "Who told you that!" Anyway, I got it fixed up, installed the proper ground and it's been a done deal for years. The bottom line is that ground return power will try to find the battery and what ever is close to an under sized wire or path of least resistance will melt right along with it. Good Luck.