Amp Meter ByPass

I am installing a big stereo in addition to other things like an MSD box and electric fans. Plus I got a deal on this single wire PowerMaster that was new in box. I did a relay kit for the headlights already and while I haven't had a chance to drive it around at night to test it I'm hoping thats the fix the my headlight flickering.

So I looked at the MAD page before I posted this thread and I'm just not 100% sure what wires I need to keep/cut/upgrade. My understand is with the one wire I was under the impression that I just run one wire to the battery positive. I was going to do that with 4ga wire and a 150 amp fuse. Now is there wires coming from the starter relay that are going into the bulk head connector that i'm to replace? If I could I would really like to keep the factory amp gauge but It sounds like even if I up the wires to the gauge its a fire waiting to happen if I throw 140 amps to it.