Make sure you get a wiring diagram first. Once you do so, get your essentials wired i.e. live, earth etc. Next get a voltmeter, tap the live to the signal line and the earth to the chassis. Press the button relevant to the signal. You should get a small increase in the power flow. This will ensure that you wired the basics properly.
Next, locate the relevant wire using the wiring diagram and splice it in/ follow the instructions as said. With each new signal wire, ensure you test it before moving on. If you encounter a problem, its easier to fix if its in steps as apposed to blitzing it all out at once.
