Here are some truisms:
A 120 amp alternator with a decent voltage regulator puts out exactly the number of amps the system requires.
CORRECT
A 120 amp alternator will put out up to its rating if you load up the system.
CORRECT
Throwing 120 amps at a 37 amp system loaded more than its capacity WILL cause any weak spots to become obvious, as the magic smoke escapes into the air.
will mean the wiring and connections are underrated by the systems requirement, but not an alt fault. When the alt is not enough the batt will provide the lack of power from alt ( discharge reading ). So the load remains the same, just the source changes. And still will mean is underrated.
This becomes worst when the batt is discharged, which will add MORE LOAD to the system. THIS is the failure. We need to keep the batt out of the play becoming on a load sucker ( charge reading ) after being sucked out
so... if your car sucks average 25 amps at iddle and the alt just sources 18-20 amps while iddling, the rest of load ( 5-7 amps ) will be provided by the batt.
Once you rev up the engine, the batt becomes on part of the sucker system, so your car is NOT anymore a 25 amps sucker, but mostly sure the full alt output... 35 amps. But 10 amps takes QUITE LONG to get recharged the batt on the car. This is what gets stressed the system, coming and going.
conclusion... an alt able to feed everything at iddle, and reinforce the wiring up to ammeter... done. The car will keep sucking the same load, the batt won't suck anymore because won't be sucked anymore, and will ge an stable power system
AND NOTHING hooked to the batt, because this will be read by the ammeter as a charge, being not a charge
