If keeping ammeter and planning to keeping reading correctly, you SHOULDN’T wire anything into the batt side.

I never said wiring doesn’t need to be upgraded or at least adviced, but there is a just one correct way to make it keeping the ammeter working correctly and is not linking the batt and alt with a jumper wire

BTW, you can install a 500 amps alt, but if the car just sucks 45, the amp will provide just that. Amperage is demanded by the accesories, not simply put out by the alt by its own.

You feed with the same battery the map light with a 18 gauge wire than the starter motor with a 2 or 4 gauge wire. The wiring must be matched with the device to be sourced, not necesarilly with the source capacity