I have an '87 GMC R2500 Suburban with some fun power lock issues. The front two doors are fine, they lock and unlock normally. The rear-seat doors don't do either, and the barn doors lock but don't unlock. I'm hoping to get this fixed before too much longer since its getting annoying! I haven't ripped things too far apart to check yet since it looks like it may be quite 'fun' to do, so I wanted to ask opinions first on possible causes. Thanks in advance!