I have a 1999 dodge ram with the infinity sound system. It had the stock head-unit in but it was all messed up and buttons malfunctioned. Also the right speakers didn't always work, and the left rear one never worked(but i do not believe it is blown). Well anyways, i figured it was the head-unit, so i switched to an aftermarket one. Buttons work how they are suppose to, however, left rear speaker still doesn't work and the right speakers seem to only work when the truck is running? Any Ideas??
Thank you

 

The infinity system has amps at the front speakers, most aftermarket head units have no provision to power them, and they also do not have pre-amp outputs, which is what they are going to want.

Try a different speaker in the rear. See if it works then.

 

Search this forum for "Infinity speakers" and you should find plenty of info on bypassing the amp on the speaker.