I understand why you would use this method but in a high vibration application, a car, tinning the wire is not recommended. If the harness is being made is for use in the home only, with no chance of it ever migrating to a car than soldering is fine. The reason for using a crimp is to allow the
wire to flex. When the wires are soldered to the connectors and not held by a strain relief they will eventually break off. I would suggest that if you wish to make your own connections that you buy or borrow a crimper. The solderless needlenose method will produce an inferior crimp but will work in a pinch. A cheap crimper can be had at radio shack for under 20 bucks. A good ratcheting crimper can be purchased through a number of electronic warehouses for around 100.