Wiring fire, advice sought!

I am in the mist of the mad electrical upgrade and I noticed on their diagram they totally bypass the amp gauge. Can I get an autometer voltmeter and use that or do I need to solder the red and black wires together because on the mad electrical site it states

"we will make use of both legs of the old AMP gauge circuit–because it doubles the strength of the main power-up circuit to the “welded splice,” which serves as power distribution. "