No Sound in Right Side Speakers

[quasi mofo]

I added some sound damping to my car and realized that I have no sound coming from my right side speakers.
I have a 1989 325is with premium sound. The stock speakers and wiring are in place, but the BMW amplifier has been removed. After pulling the trunk liner and the aftermarket stereo, I found 3 RCA cable pairs that run from the dash to the trunk and 3 runs of stereo wire. One of the stereo wires terminates behind the stereo and two were coiled up under the rear seat.

As a novice E30 archeologist, I'm thinking that one of the PO's replaced the stock head unit, pulled the stock amp and bypassed the stock wiring with an aftermarket amp and new stereo wire. I guess they were using a 3 channel amp, maybe. But then a more recent owner pulled the aftermarket amp and reused the stock wiring. This is where I seem to be having a problem. As you can see there is a nest of wiring behind the stereo with butt connectors for days.



So in the second image, the PO has the green and purple right front/rear speaker wires connected to yellow/black and blue/black wires at this second harness. The negative green/black and purple/black wires aren't connected to anything.

Any advice on what I should to do restore sound to the right side speakers? Thanks in advance!

[reelizmpro]

Obvious thing to check is the Balance control on the headunit. Then find the right speaker wires coming from the headunit and verify output with a good speaker. If the headunit amp right channel outputs are good, check the speaker end of the wiring for output. If you have no output at the speaker end, the problem is between headunit and the speaker...most likely at the amp bypass in the trunk. In the process of troubleshooting you may find bad components or just a bad connection somewhere.

[quasi mofo]

Just to clarify, there's no amp bypass in the trunk that I can see. I'll pull the rear seat again to check the wiring back there.
I wired up a new head unit replicating the connections and get the same result with no sound to the right side speakers.

Can you all spot any issues with the weird second wiring harness? This seems strange to exclude the purple and green wires from the connections.

[reelizmpro]

Just to clarify, there's no amp bypass in the trunk that I can see.

You have an 89 325iS with premium sound and aftermarket stereo. Unless someone ran aftermarket speaker wiring...they bypassed the amp in the trunk. This is how you are able to use the stock wiring. The fact that your left side works with stock wiring, means they bypassed the amp. Look at the remaining amp connector in the trunk and it's wiring for splices.

From your pictures I only see the stereo harness attached to OEM wiring for your mids/tweeters. You don't show any aftermarket wiring but if you have RCA cables running back there then they must have had amps in the trunk at some point. It could be remnants of an old system. Also, the aftermarket harness on the stereo may have some optional features that may be left disconnected if unused.