They have a wiring kit for trailer, proper color codes. For long term
I would go that way. Solder and heat shrink. If you live where they
treat the roads in the winter, any exposed wire will corrode quickly.
The speaker wire is not made to flex. The cover is not made to handle
heat.
Any auto parts store will have what you need, and in the long run it
will save you time and money and be much safer for you and others.
http://www.harborfreight.com/four-wa...kit-96658.html
Another point, if you have a later model car, 2000 and up, you need to get a harness
for the car as well. Cutting and splicing in the cars harness can cause major problems
with the vehicle. The one you need is made for your car and no cutting is needed, just
plug it in per instructions.
Some cars come from the factory with the wiring in place. On ours it was hidden under
the trim panel in the trunk.