i recently installed a alpine head unit in my 95 monte carlo dd and whenever the radio is on the speedometer doesnt work and if you turn the radio up the speedometer bounces with the music if i turn it off the speedo works fine....i moved the ground to a better location ....i was thinking do i have to run a power wire from the battery to the headunit thanks for any input

 

What double din model did you install? If you installed a unit with navigation where you had to tap the green/white wire for vehicle speed sense and you did so behind the instrument cluster, that is where the problem is. GM's cannot be tapped at the speedometer input at the cluster as it causes all kind of interference (usually gas guage problems though).

 

i installed a single din alpine idx-200 i think its an ipod only headunit no cd player and i had a harness adapter so everything was plug and play just had to connect wires to headunit and i had a wire diagram for it, i dont have any idea why its doing it i was just thinking that it was power related any more suggestions would be appreciated