Originally Posted by NachoRT74
Originally Posted by poorboy
Originally Posted by A12
Originally Posted by 5thAve
60 to 65 is no big deal. They usually upped the wire size when it was a fleet car with an HD alternator.


Don't they all just regulate to 12v - 14v +/- a volt or two? Is there a heavy duty wiring harness, never heard of this???


There definitely is a heavy duty wire harness, but I don't think it shows up until you get into the high amp alternators. Higher amps require larger gauge wires. The + battery wire is thicker gauge, and many have a ground for the alternator built in.
As more electrical accessories that were added to the vehicle, higher charging system amperage was needed to keep the battery charged. Things like power seats, power windows, Ac, radios with power boosters, and additional lighting all added to the battery current draw, the charging systems had to be stepped up to carry the extra load. More electrical accessories added up pretty fast in the late 60s and early 70s, then when the on board computers of the mid to late 70s showed up, charging systems went crazy. 90 to 120 Amp charging systems was not uncommon. The old wiring harness could never have handled the power flow.


Wiring is stablished by the load requested by the system or device, not by the source.

At you home you plug your cell phone charger on the same outlet than your iron. Source is the same outlet on wall, but iron get a thick wire, while cell phone is barelly some hair thick copper strands.

Your starter motor gets a 2 or 4 gauge wire, while the other wire is 10 or 12 gauge. Both on same battery ( 450, 500, 700 amps battery )


For that example the wiring on the device might be established by the device but the wiring to the plug is established by the system. If it's a 15A outlet you are using it doesn't matter if you're plugging in an iron or a cellphone the wiring to the outlet still needs to be sized for 15A.

The positive wire for a 120 amp alternator is bigger then a 60A one because there is a potential of having more load on it.