Car PC INstallation Wiring

I am planning to install a car pc with which i want some wiring advice. for the power supply (90watts output & 6 to 12v input), it needs 3 connections, 1 for 12v, 2 for ground and 3 for ignition. now if i run the 12v and the negative direct from the battery, can i tap into the ignition wire connected to my head unit to run the pc also? in other words i would solder 2 pieces of wire on the ignition wire to run both the head unit and the pc. would that be okay or would the load be too much for the ignition wire? also what amp fuse should i use inline for the 12v connection?”

I personally wouldn’t use the ignition switch for anything other than what it was designed for in the car. I would wire it all direct from the battery, and if you want to put a toggle switch on ones you want to turn on and off (just like the ignition switch turning on and off.) Cars ignition switches get power surges when the car starts and it could mess with your computer. As for the fuse amperage, 90 Watts is a lot of power. I would use a 25 amps fuse for protection.