If the stereo volume only works with the steering wheel is this more likely an issue with the stereo or amplifier?

 

Has been a known issue with the volume ****. It's the head unit, not the amp. I don't remember if there's a fix or not.

 

The cause is dirt inside. You can clean the internals of the volume dial. I did that and it worked for a while, so it's not a permanent solution. You have to pull the head unit, open it, remove the front cover and then you can pry open the potentiometer by bending the tiny metal tabs gently. Clean the internals with a swab and alcohol.

The sustainable solution would be replacing the potentiometer. Unfortunately I haven't found it from a parts store yet.

 

When mine did that it signaled that the head unit was on it's way out..