Thanks for the link.

I disconnected the head unit this morning to prevent any potential damage. Hopefully I will have some spare time this weekend. I will bypass the fader switch and wire all eight of the speaker wires in the body directly to the eight speaker wires from the head unit. Then I'll see if I still have problems.

I'd rather wait and not have to rewire or replace the speakers for now. I just want to be able to have the volume loud enough to hear my music well at all speeds. I may replace the factory paper speakers with some new Blaupunkts or something if I can find ones that fit. I may rewire the speakers if necessary for better sound/volume/head unit longevity.