ute-73bt

I just installed a new ute-73bt. It replaced a cde-133. The amp and sub worked beautifully before switching the head unit. If I connect the amp to the lower, dedicated, sub rca connection I don't get any sound from the sub. If I connect the amp to the upper rcas meant for front and rear speakers...

Hi everyone, I'm hoping someone can shed some light on my situation (probably fairly obsolete these days) Quick rundown of the parts: Ford E250 camper - has "common ground" speaker wiring. Only one ground is shared between all speaker positives. Alpine UTE-BT73 head unit - has "floating...