Now you have me really confused. Are you saying that you had a 3-amp fuse in the main fuse holder in the battery line? Or an 8-amp fuse? What led you to do that? If you turn on a bunch of lights, I would expect either to pop. Each dual light fixture takes more than 2 amps, so if you turn on 2 or 3 of them, you are done if you install an undersized fuse.
I have no idea what "started a fire in my buddies garage" means. What actually happened?
Way back in your original post, you said that you experienced a short that blew the main fuse, which was presumably a 30-amp fuse at that time. I am now thinking that the short not only blew the fuse, but also overheated the fuseholder. I don't have many pet peeves with TM, but that fuseholder is one of them. It is quite intolerant of even normal loads, and it is common for it to overheat (often indicated by one or both ends turning brown). At that point it loses good contact with the body of the fuse, which causes more heating, and the fuse can pop not from an overload, but just from the heat. As Keith mentioned, many of us have replaced that fuseholder with a flat automotive blade-type fuse and holder.
Finally, a "3AG fuse" is not necessarily a 3-amp fuse. The designation "3AG" refers to the body size and style. But 3AG fuses come in a wide variety of current ratings. A quick hit on Google might make this more clear.
To reiterate, you should have a 30-amp fuse in the main fuseholder at the battery - no bigger, no smaller. And I think you would be wise to install a new fuseholder with a blade-type fuse. If it's not clear what I am referring to, see a picture in this thread.
http://www.trailmanorowners.com/foru...ead.php?t=7760
Bill