splicing the factory wiring already are we
doing that in a car is quite different than doing it in a console.
Be sure to solder all your splices then use waterproof heat shrink tube and then wrap it in electrical tape for good measure. anything less will cause corrosion and rust which will lead to faulty wiring down the road... remember, cars are a VERY harsh environment, ridiculously high and low temperature, lots of vibration, quick shocks and movement, water, dirt, potentially oil and sludge, etc... everything you do needs to be protected from those things.... not to mention the power source for all your electronics is quite unreliable and swings wildly in terms of the power it's supplying.