Electrical systems hate crappy wiring jobs. Most installers use clip in pieces or they cut the coating and wrap the wire around on the outside. Both suck for connections. The way to do it is this.. take the coating off about an inch of the wire, use a pick to make a hole through the strands (not breaking them..just making a hole through) then put your wire that you are adding through the hole, crimp it back shut with needle nose pliers, solder it well and then tape it up.
That's how my install was done (by me) on my Regal. Never once had any issue.
