Sony MEX-BT4100 in 2002 Explorer subwoofer pop
This install went like a breeze with a Metra adapter harness until I first powered and the factory sub (2002 Explorer Limited with partial Mach 460 system) popped on power-up.
No search results on the web for my problem. I hope this post will help someone searching in the future. I really appreciate the help I got from searching this forum for harness color coding links and general install info.
I checked all of my wiring and tested resistance between grounds and car chassis and everything was connected properly. The sub still popped on power up when I had it disconnected from the Sony and it's input RCA connector shorted. The only other connections to the sub were factory power and the Sony remote ON.
I tested the remote ON voltage with each radio connected: Sony was 12vdc and Ford was 5.8vdc. I decided to drop the remote voltage as the next step. A 2.21K resistor dropped the remote voltage to 7 volts and the pop was gone. I figure that the sub remote on input is not rated for 12 VDC and the circuit was swamped dumping into the audio path.