Static electricity shock and the no sound from all speakers

Just installed an amp and sub using high level inputs since I have a factory stereo. The explorer is a 96 with a stock cd/cassette from a 2000. I have bypassed the factory amp. I tapped into the speaker signals for the new amp in the back by splicing into the factory amp bypass harness. The amp has a ground on the high level input harness that instructions say you may or may not need. If I connect this ground, I get no sound from any of the speakers. I disconnected the high level harness ground and everything works...until I get out. Sliding across the seat builds up static and I get a shock when I touch the door. As soon as this happens, all the speakers shut off. The amp and head unit still have power. Just no sound. If I unplug the high level harness from the amp, the stock speakers start working. Plug it back in and the sub works until I get shocked again. Wtf is this?

The sub amp isn't grounded properly, or your chassis grounds are bad somewhere.
Never heard of something like this happening with a hi/lo converter.

I removed the high level harness from the amp and installed an RCA converter. Everything is working properly now but I'd prefer to just use the high level inputs on the amp. I installed the high level harness by tapping into the positive and negative wires for the rear speakers. I might try it again using just the positive wires from the speakers and the ground from the high level harness.