Why do the LATCH installation instructions state to connect one of the connectors before routing the LATCH belt? 

The LATCH connectors are “handed” – meaning that there is only one correct orientation for the LATCH connectors and the adjuster side will always end up on the side of the seat closest to the passenger side of the vehicle. 

The LATCH belt will need to be removed from storage and routed every time the Liingo is installed, so the instructions were written in a manner designed to provide a systematic way to end up with the correct routing each time.