On my car I am just running two 10-AWG wires.
One wire to the original alternator wire, and the other directly the the starter relay.
This basically puts them in parallel, but the direct wire will have slightly less resistance so it will see most of the load. In theory the amp gauge should work, but take twice the current for the same indicator position. Even though I have a 136 amp alternator, I got it mostly for the improved low speed output and better bearing design. It's rare if it has to output more than 40-amps. The parallel wiring also reduces the current through bulkhead connector.
Both lines must be fused, and if one fuse goes the other will be taken out too. I like the fuse with the holder. Not sure how long it takes to blow the fuse? The fuseable link allows excess current for a short time before it burns out. Either way, all it is really protecting is the wiring to/from the alternator.