2002 Saturn SC2 Charging Issues.

The gauge of the link is not the issue. AC generators can only produce the amount of current needed by the electrical system, and during a full-load test, they are physically incapable of producing more than their design value. The most common unit is a 90 amp generator. Under normal conditions your 12 gauge fuse link will be sufficient. It's during a load test that its current rating can be exceeded, however, fuse link wires are used because they take a small amount of time to burn open to reduce nuisance problems, and load-tests only require running the generator wide-open for a few seconds. You don't even need a load test to tell if the charging system is working. Simply measuring battery voltage with the engine running will do it. It must be between 13.75 and 14.75 volts.

What you described is commonly caused by worn brushes inside the generator that make intermittent contact. Only Chrysler provides easily accessible test points to diagnose that. Ford had a pretty nice design during the '90s, but they stopped doing that. GM had a real nice design through 1986 that had a nice test point, but they dumped that in favor of the world's worst design starting with the '87 models. There's no test points, and even getting the generator apart is a lesson in major frustration. The best you can do is measure the voltage on the large output terminal. You must always find the same voltage there as across the battery terminals. If it's higher with the engine running and 0 volts with the engine off, then look at that fuse link. If you find around 12.6 volts with the engine running, suspect the brushes.

Obviously I can't argue with success, and I'm happy it's working, but I'd be willing to bet there was something else going on. That fuse link wire is meant to be the weak link in the chain, and a 12 gauge wire is the correct size on a vehicle with a smaller generator and smaller wiring. Your generator won't produce any more current than the vehicle needs. In fact, you'd never know the difference if you had a 90 amp generator instead of perhaps a 120 amp unit except for the very few instances when you really need more current.

In my electrical classes I often compared electrical current flow to water flowing in a pipe or river. In effect, what you had was a smaller diameter pipe. That would cause the resistance you mentioned, but if you only needed a little water flow, the diameter of that smaller pipe would have no affect on on flow. You'd still have something, not nothing.

The exception would be if you tried to do a full-field load test on the charging system. If you drew the maximum current the generator could deliver for say 10 or 15 seconds, it could be possible to burn the fuse link open, but under normal conditions the smaller wire wouldn't cause a problem. The entire wire from the generator to the battery is likely to have two or three ohms of resistance anyway, and the smaller link would add less than 0.1 ohm to that total.

My other concern is you said the problem was intermittent before, and it worked for a while with the smaller fuse link. I hope it stays working, but if not, holler back and we'll dig into it further.