The wiper motor is the only system on a LC that I can think of that switches the ground. It's just a little different in that the switch is on the other side of the motor. Power in, power out to the switch, ground after the switch.
I have always used rosen core. Acid core shouldn't be used with...
THe first part of your question is easy. There are juction connctors and you can put multiple wires in one side of a crimp connector and they do make connectors that take three wires. My favorite is one made by 3M that has three holes in a row that are pierced by a steel clip. Overall, I hate...