I have 2007 dodge ram cummins 3500. It has the infinity system with infinitiy amp. I recently tried installing a aftermarket radio. The jensen radio was bought from eBay and was said to plug play for exact model. I pluged it up and the radio works but no sound. Played with it and played with it. Nothing. then out of no where it played for about 2 mins and then I shut the truck off and turned back on. back to nothing. Can't figure why door speakers won't play or what im missing.

 

It's because the amp is not being turned on by the new radio. If the radio has a power antenna output use that to turn on the amp.