Will resistance in the charging circuit increase the alternator's output voltage? Sure, voltage regulators are imperfect devices and you'll get a higher voltage across a high-resistance load than one with low resistance.
However, there's a serious problem with your theory: If the resistance was high enough to cause a measurable rise in voltage, you would have had starting problems. Do the math: When the battery is fully charged, the charging current is only a few amps. Let's be generous and say 10 amps. A one volt rise translates to 0.1 ohms. But that same one-tenth of an ohm is present during starting. So let's say it takes 200 amps to crank over your engine. 200 times 0.1 = 20 volts. Oops! We only had about 12 volts to work with. I don't think that engine is going to turn over with a tenth of an ohm in the circuit.
Here's the deal: Voltage regulators are temperature compensated. The hotter it gets, the lower the voltage. That reduces overcharging while ensuring a rapid charge after starting. If you watch the voltage from a cold start until you've been driving for half an hour, you'll see the voltage slowly drop off. It'll probably start out close to 15 volts and drop down to less than 14. That's just normal behavior and you'll see it in any vehicle with a voltage regulator.
This post was edited by MarkB_MI at 03:46:57 10/25/13.
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