Alternator started sparking

After trying to figure out the voltage drop when I turned my lights on, my alternator is now only putting out 12.4, basically matching my batteries power. The only thing I did was bypass the 3 prong connector for the front marker light. The connector was old and brittle, so I clipped the wires and connected them directly. That’s the only change I made. While searching for possible issues, I changed out an old fusible link. Nothing changed. I started looking for possible issues and ended up finding out that when I use my brake pedal for a ground, I get a 1.7 volt drop, compared to every other place I ground on. I don’t f’n get it.