Car Stereos: subwoofer, amplifier power, rear speakers

Question
hello
i have a 1990 ford f150 and were upgrading from a  facotry stereo. we installed a headunit and new doorpanel speakers. it doesnt have rear speakers. we bought a amplifier and a 10inch sub. we ran all wires correctly,  rcas  are hooked up correct ground wire remote wire etc. the amp powers on fine but i get nothing from the sub. to make sure it wasnt the amp or sub i tried a different amp and sub  same thing. amp has power but no sound or anything from the sub. we checked all fuses and rca  hookups again and cant figure  out why it wont work. any pointers?

Answer
I suspect the line level converter may not be working... You will need an mp3 player and a 1/8" to rca adaptor to test this. Start by plugging an mp3 player directly into the amplifier (power it up after you make the connection so you dont get unnecessary pops) and see if the amp plays. if it does, there is a problem with the converter. You may want to get it tested by a qualified installer.