I have a MSD 150-160 amp 1-wire alternator on my Challenger and it keeps the voltmeter pegged at 14 amps when it's in park after startup (approx 8-900rpm) no matter what the load (electric fans/aftermarket stereo/ignition/elec. fuel pump) the second I put it in drive the volts drop to just above 12 unless I crank up the rev's(1,500 plus). Seems weird to me, in park takes all it takes all the electrical load i can throw at it, in Drive same rpm struggles at just over 12 volts, until the rev's come up. I do have the march underdrive pullies which I am regretting.

14 volts?

I going to assume you mean 14 volts not 14 amps. Below is just my personal opinion and experience with one wire alts.

A ONE WIRE alternator is best suited for applications that need the alternator only for a battery charger. They really don't work well with many accessories.

Just a little tech about the one wire alts.

After the engine has been started, and the alternator is spinning, the existing weak magnetic field from the iron core material will cause the alternator to produce a small amount of voltage. This small amount of current is used to turn the voltage regulator electronics ON (rather than wiring a special wiring circuit to turn the voltage regulator ON like the factory did). The faster we spin the alternator, the greater the potential for output. Sometimes you have to rev the engine once to kick in the alternator. (You have to spin the field in the alternator fast enough to make sufficient current to turn ON the self-exciting voltage regulator.) Other times what happens is in park or neutral the eng rpm is high enough to kick the alt in but once you put it in gear and the rpm's drop the alt will turn it self off and you are running on the battery. Pending on the ign system and accessories you are running you might be discharging the battery fairly hard and even though you bring the rpm's back up driving it might take 15 minutes of driving to bring the battery back to a good state. But that can also vary because load on the electrical system.

On a side note running a smaller then stock pulley on the crank or larger on the alt will also change the alts output. I have seen more problems with under-drive pulleys then I can think of.

Sorry yes I meant volts. I am tempted to just toss these underdrive pullies already I think that may be the source of a few problems. I didn't realize the alternator could "unexcite" itself if rpm dropped after it got excited.