When you disconnect a car battery, you take off the black then red right? I dont want to kill myself doing this.

 

If you are just disconnecting then removal of the negative (black) is all that is required and is recommended for long term storage in the FSM. If you are going to remove it completly then remove the positive al well.

 

Im installing new headlights, but i gotta splice wires together. So should I just remove black?

 

Yes thats all thats required.