ext cab speaker

I just bought a 2000 ext cab and the left rear speaker does not work. I pulled the factory radio out and put it back in and it started working off and on. I switched the radio but cant get it to work at all now. I tried to chase the wires down and everything seems to be ok. Can someone give me an idea of what i should do now?

When you changed the radio did you splice into the factory wires or use a plug in connector it is possible the problem is in the factory radio connections also try finding an extra speaker somewhere maybe you have a small sterio in your house borrow a speaker from it and try jumping the connections with the wire from the home speaker see if you get sound if you do replace the speaker in your truck