I recently acquired an 89 tbird with the stock premium sound system. I purchased a new head unit and am having difficulty. I purchased the correct adapters for the sysyem. However, I'm not sure what to do with the ground wire from the speaker connector. I have the stereo hooked up and it sounds great but I have no instrument panel. I'm sure it has to do with the ground wire. I temporarily connected the ground wire to a spare ground on the power harness. Does the ground wire have to be grounded to the new stereo? any advice would be helpful.

 

Most of those older audio units had a replaceable panel illumination bulb.. Think it was a #37.. Looks like a standard 194 onlysmaller.. Lift the top panel off the audio unit and there should be a bulb socket facing towards the panel.. Twist it slightly and pull the socket gently out.. Some are distorted from heat over time, more so if the bulb had been previously replaced with a #74 (higher candle power) I'm pretty sure they were a #37 though if my memory iscorrect..