jvc KD-R650 in 1979 z28 camaro problems

[79z28]

I installed a jvc KD-R650 head unit today, I have two 100 watt rear speakers in my 1979 z28 camaro, no front speakers. I've hooked up many stereos through the years, this one has me stumped. after the install, I set all my settings, and clock, bass, treble, etc. The unit sounded great on accesory, but when I started the car, the unit started breaking up, skipping words, on CD and on FM. I shut car off and put key back on asesory and it played perfect WTF? I switched the switched power wire to full time power, no help, I tried both power wires on switched power, no change. I ran a totaly seperate wire from the battery, and hooked it to switched and full time power wires from unit, no change. I cleaned and moved the ground wire, no change. I tried two different speakers, no change, now when the unit is messing up, the units face lights do not flash on and off with the music, it stays on normally. Just the music skips and breaks up. It's a brand new unit not used. The battery and altenater are good, there's plenty of power, I don't have an amp, I just don't understand why starting the car messes it up. HELP!

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[brian84corvette 10+ year member]

run new speaker wires to the rear speakers... and or test with diffrent speakers back there. could be a bad conection with engine running causing it to shake around a little ? or just crappy old speaker wires from 1979 that are shorting out somewhere ?

 

[79z28]

! ran new speaker wire, I tried new speakers, no change, I'm begining to think that the head unit is bad. I just can't see why starting the car makes the audio break up, and when the car is shut off it plays perfect. what could be different when the car is running? I even ran a hot wire from the battery, bypassing the wiring harness and it still messes up when the car is running. I mean 12 volts is 12 volts whether the car is running or not, It's not interference noise coming through the speakers, the audio on cd and fm start breaking up, like you only hear every third word. You know how when your digital signal on your tv cable starts breaking up and the sound is all messed up, that's what it does.