I have a '98 ES300 that I bought without a head unit. Previous owner took out aftermarket HU, Amp and subs.

I put in a new HU: Pioneer DEH-X5600HD (50 x 4 outputs) using the 70-8113 harness(with RCA plugs). I found out after, that the speaker wires for the factory amp were all cut and rewired for the aftermarket stuff from the previous owner. I repaired the amp wiring(solder + heat shrink tubes), and now I get very very low sound from the 4 door speakers and low sound and popping from the sub.

I'm being told its a conflict between the new head unit amp and the factory amp. Why then would I have bought the "Factory amp integration wiring harness" if this was going to be an issue?

Have I been misinformed? If so what could I troubleshoot to find the culprit. If this is correct information, what do I need to do to get a working stereo system.

Thanks in advance.

 

You need resistors to cut out the interference from the stock amp....ground loops