I have a 2001 pontiac grand prix gtp special limited edition and it has a good stereo in it but only when tbe back speakers work. They are supposed to be built in tens with amplifier in the trunk but they seem to want to only work when they have direct sunlight on them. Is there sny way to fix it so they always work? I've checked the wiring to make sure everythinh was conected snd it all appears to be.