I have a Subaru outback, and I had some trouble installing new speakers on it, but I eventually managed to do it. I also replaced my tires on it, and while I was working on the car I decided to get the speakers out of the way too.
Connecting speaker wires is typically done with a simple twist and maybe one wrap of electrical tape. There is a much better way to connect speaker wires in your car. This connection method is no more difficult to use.
A much higher quality of sound can be produced by using a soldered connection. This connection will also have better physical strength. An expensive soldering iron is not needed if you only solder speaker wires occasionally. You can probably get a small soldering kit for less than 20 dollars. If you buy the soldering gun separately, make sure you do not forget the solder.
Heat shrink wrap is a plastic tube that resembles a straw. You slide it on the wire connection and apply heat. This can be done with the flame of a cigarette lighter or a heat gun. You might even be able to use a really hot hair drier. When heat is applied the plastic tube shrinks giving the wire connection both strength and protection.
First trim the insulation off both wire ends to be connected. Then slide a piece of heat shrink tube onto one wire and move it back out of the way. Twist the bare wires together in a neat way. Fold the twist back against one wire. Do this before soldering to set the bend into the wires for later. When you are ready to solder raise the twisted connection away from the wire a bit.
A bit of improper soldering technique is called for here. When soldering light speaker wire it is easy to melt the insulation if soldered with proper technique. Rather than heat the connection until it will melt solder. Add solder directly to the tip of the soldering gun. Once you have a drop of solder formed on the tip of the gun. Touch it to the wire connection and hold it there. In a second or two the wires will draw the solder up into the twist. That is all you need, once the solder runs into the twisted wire take the soldering gun away.
Allow the soldered connection to cool for a few seconds before you touch it. When the connection has cooled down bend it back to the wire to make a nice streamlined connection. Slide the heat shrink tube upon the connection and center it. Apply heat to the heat shrink tube. Heat the entire length of the tube and ensure even shrinkage.
This type connection is not prone to break due to vibration over time. The superior sound quality comes from a solid wire to wire connection. That is better than a single point contact that a crimp connector will give you. When done properly this type of connection is very stream lined and looks really nice. This is the best way to connect speaker wires in your car for physical strength and really clear sound quality.