Rigging Armor to Player I've recently been modeling some armor and decided it was time to see my work in action! Spent a good portion of yesterday reading online, searching tutorials and this seemed to be the most recent one I can find with the most checked answers. 

https://stackoverflow.com/questions/34719718/transferring-rig-weights-from-one-mesh-to-another-in-blender-2-76

What I did was Parent the shirt to the rig, deleted the vertex groups and un-parented the shirt from the rig. ( was that correct? the first paragraph is a bit confusing ) Next I added the data transfer modifier, selected my players body as the source, chose vertex data and selected vertex groups, then pressed generate data layers. When switching back to object data tab, I can see a list of bones in the vertex groups. Last I selected the Shirt, then shift selected my rig, hit ctrl p and parented with empty groups. I also tried applying the modifier before and after I applied the groups, the result is always the same with the characters shirt ending up being slightly inside the players body / behind his back. I can get the shirt to be back on the players body by moving the armature modifier to the top position but the shirt is still not rigged to the character. Also If I apply the data transfer modifier the shirt just ends up going inside / behind the player again. I've tried many different tutorials, all usually ending in the same result. I've never gotten anything to follow the armature of my characters. Am I doing something wrong or completely missing a step? Is this just an outdated tutorial?
What I usually do if I can't seem to get things right in this case, is delete all the vertex groups and armature/mirror modifiers (or any other mods that might affect things) from the shirt and try again. If you have existing vert groups on the shirt it may cause problems. With a "blank" shirt, add the data transfer modifier again, apply it, then add the armature modifier back on.