I've got years of experience working with vehicle electronics, down to making custom harnesses depending on the setup.
If you've got sound system questions, ask. electrical issues, ask. I can more than likely figure it out for ya or point ya in the right direction, last but least I can freaking come fix it for ya.
First one I'll start off with is aftermarket gauges. I'd say a majority of 95% of new gauge designs today require 12v ignition, ground, illumination (50/50), and any other connections for datalogging or ems systems.
You have 2 types of gauges, mechanical and electronic.
Mechanical - works in reference of actual readings from an installed sensor or sensor line tap. Most times preferred for water temp, oil temp, user preferred pressures.
The cons are that when they break, oil pressure gauges and fuel pressure gauges become a hazard inside the cabin as they can leak at the gauge if it's the known broken part.
Electronic gauges work by using a sensor and using wiring as the sending portion, to eliminate the running of hard vaccum tubing or in a sense an excessively long line, instead electrical signal can travel thousands of milliseconds faster plus also allow the benefit of multiple mounting points for the sensors in some cases.
The cons are that electrical gauges can go bad and even worse can if installed wrong will damage factory wiring if you are tapped, they require a little finesse when installed sometimes.
If you have any questions about gauges, ask away. There are practically tons of them available, all the way to where you can customize the layouts, colors, size, even the installation diameter.
sounds like a bunch of yap, boredom yes, but to help the not so electronic savvy I might as well help. I've seen on a few occasions of where a simple install doesn't look right or isn't working right.