Twelve-volt work is where a lot of vehicles get ruined by well-meaning shortcuts. We install and service remote starters, audio systems, lighting, accessory switching and marine 12-volt systems using proper connections, fusing and routing.
That includes diagnosing electrical gremlins from previous installs, adding accessory circuits for plows, lights and winches, and wiring boat systems that have to survive damp and vibration.
Remote starters have their own page with more detail on how an installation works and which systems suit which vehicles.