So I have a Sundown 100.2 amp powering two Memphis 10" subs in a tech12volt under seat box in my Nissan Titan. It has been working fine for over a year now. One day last week it stopped working and I just got around to it yesterday.

Fuses check out. Amp is getting power. Subs wired correctly and are in a 4 ohm bridge setup. Good grounds and connections, and there is a grounding kit on truck.

Noticed the "protection" light is illuminated and continued the troubleshooting.
Used a multimeter and tested all voice coils on the subs, they read correctly.

After continued testing the sub immediately goes into protect mode whenever the RCA cables are connected to the input jack. It does this with or without subs connected, or source playing. I even ran the RCAs from my front speakers to the amp and it did it as well.

Looking close it appears one RCA jack is loose. Not sure how that happened, or if it’s always been that way. I use 90 degree connectors and give plenty of slack to eliminate any strain on the jacks. With a car seat on top of the seat, nothing has "touched" that area in 7 months. So I’m still not sure what caused it, and the system is almost always at a low level.

I did the generic “contact us” thing for Sundown on their website. Was wondering if anyone else here had any suggestions on other things to try?