It did it immediately after first powering up the system, so I doubt the amp is shot. The angle grinded part is pretty smooth, but I drilled through the ring terminal to make the hole bigger to fit around the seat belt bolt, effectively reducing its contact patch with the chassis. Is this most likely the problem? Should I get another ring terminal and find another place for the bolt where I don't have to drill a bigger hole through it?
dont take this as condescending, as i don't know what your experience in the hobby is, but i like to be somewhat thorough with explanations for idle readers just scratching the surface.
well, we know that electrons transfer on an atomic level, so even the slightest thousandth in deviation of surface contact between two will affect such. that being said, it is my opinion that finesse should be observed when surface prep is needed.
even if you barely touch it, a grinding wheel not affixed to a stationary armature of sorts with incremental adjustment onto the work surface (i.e.; surface grinder) invites uneven variations in material removal as you cannot attack it at the same angle and equal pressure on a linear plane over the exact same stroke distance every stroke. wire wheels/brushes and stripping wheels are made to be forgiving in the instance you apply too much pressure to it,.. brass wire wheels are much more forgiving than steel. sanding with a high grain paper is ideal, but that involves more time and labor. airplane paint remover works extremely well, but it's highly toxic and would never recommend using such inside a car without ample amounts of ventilation and a respirator.
burrs on lug rings would seem negligible and not important as the burr usually displaces into the ring center upon applying a good 'ugga dugga' (for lack of a better term atm) when tightening down the lug,.. at least in my experience, it does. the problem with drilling out lugs is you reduce the surface area, so yes, i would definitely find a better way to fasten it without having to do the same, if not for that, for what kush said about seat belt mounts.
without having to run an additional or dedicated ground wire (which i always do and try to convince others to do, personally), the best chassis grounds ive seen were two part configurations containing a brass block with set screw terminals that mates to a steel block fabricated specifically to be welded to the chassis, connected together with a single bolt and saw-tooth mating profile for highest contact surface area.
hope this helps, keep us updated.