Bypassing the Amp gauge - Question about the MAD Electrical method

Basically, using both the wires as shown by MAD does at least two things:

By running the alternator output direct to starter relay, you have a shorter path to the battery and less connections. You have eliminated TWO connections in the bulkhead, and the ammeter, plus "the trip back" through the long wires through the bulkhead and back

To answer your main question, by using the original black lead as they did, you now have created TWO battery "infeeds" into the car. This effectively makes one great big wire......that is the red and black are now in parallel.

I would either do it the way MAD does, or string a complete new, larger wire for the battery feed into the car.

And, ESPECIALLY if people use a "one wire" replacement alternator, the alternator charge wire needs to be MUCH larger. This is because the "one wire" is now also the voltage sensing wire.

This is one reason I used to get sideways with Dan. He claimed the MAD guys are "Chevy heads." The actual fact is, this is very well thought out using a minimum of intrusion with factory wiring.

Ma KNEW that her wiring was shaky, even back then. Google up "fleet wiring." This was done, either factory, or dealer, on taxi/ police and other cars with heavy duty alternators. The ammeter was still kept inline, but the wiring was made heavier, and was run separately through grommets in the firewall.