We have developed wiring harnesses that use aluminum wires instead of traditional copper wires for two reasons. The first is because there is an increase in demand for lighter cars due to recent increasingly severe restrictions on CO₂ emissions from cars. The second is that due to the soaring resource price of copper the industry has expectations for the advent of an alternative material for the wires of automotive wiring harnesses. Aluminum wires for automobiles have been used mainly in battery cables, where the cross-section area of the conductor is large to support high current. For the connection with terminals, special methods have been used, including ultrasonic welding and friction stir welding to ensure connection reliability of aluminum wires given that they have an insulating surface oxide film. Copper wires, on the other hand, have traditionally used a method called crimping that connects wires to terminals for automotive wiring harnesses. To apply more aluminum wires for automotive wiring harnesses, wires and terminals need to be connected by crimping. This paper will describe our achievement of connection reliability of aluminum wires and terminals that allows in-car installation by analyzing the mechanism of the crimping connection of aluminum wires and developing special terminals for aluminum wires.