+1 on Simon's advice about decent solder, terminals and crimping tool.
A decent crimping tool may cost you $25 or more but money well spent if you do the odd wiring job.
For about the same price for a box of 10 nasty insulated terminals from you local supercheap motor shop, you can buy online 50 decent brass terminals.
Get some M & FM spade/blade terminals and ring terminals and a metre of heat shrink plus your crimping tool for $50 and you'll have most of what you need for a number of years.
Tin the wire and a touch of heat and extra solder once crimped all covered with a little heat shrink and you will have a trouble free insulated connection allowing excellent current flow.
Cover with a touch of dielectric grease once plugged Inplace
