2005 GMC Envoy Radio/Speaker

My speakers sometimes work great and then other times it goes down to just the tweeter in my front passenger door. I've tried a new stereo deck and that's not the problem. Don't think the speakers are blown b/c they work perfectly sometimes. I think it's electrical b/c my husband messed with some wires behind the front passenger side door and it worked a bit more than usual but is back to not working very often. Any suggestions? Thanks.