Strawdog has the best idea. As far as those scotchloks go, they are NOT weatherproof. If it's going under the dash I would MAYBE use it. In the engine compartment they're not reliable. Over time the exposed copper in the wire and the aluminum bridge in the scotchlok corrode and you will eventually lose connection. Or worse, the wire can corrode away (I've seen it!). If you are going to use it inside a protected area, I would fill it with non conductive dielectric grease before snapping it on the wires. This keeps air (oxygen) away from the wires and slows the corrosion considerably. The special grease is available at auto parts stores, Radio shack, truck stops and plow service places.
If it's going in the engine compartment I prefer to use splices covered in self sealing heat shrink. That way they are weather tight and permanent. None of these solutions look factory so if that is a concern you need to hide them well.
