There are kits available that let you plug into your factory stereo harness without cutting the connections.
This harness is a bridge between the factory harness and the Infill harness. If you don't have one of these in your setup and the infill was either crimped or soldered directly to the factory harness I would cut the connections and replace them with male and female spade connectors
This would allow you to easily remove the unit from car and connect it on the work bench.
Hope this helps