im currently using the stock 12v wire and ground wire in my gauge wire harness for my aftermarket digital dash

i have issues with some of my digital displays when using windows, brake, turn signal, headlights. not going into great detail since it didnt get me anywehre in my last thread

so lets stick to basics

to rule out the power source and the ground wire i'm going to first try a different ground source, then if still problems i want to try directly wiring to get 12v from the battery


if go directly to the battery for the 12v what size amp fuse should i use? 10-20-30????? and put a switch on it since i dont want the gauges on when the car is off

or try a 12v ignition wire? and if i use an ignition 12v wire what fuse is that on in the fuse box?

or what else do i have for options?