charging problems

I've got a 75 D200 with a 318. I put a good alternator on it cause the old one went out. My problem is that while the truck is running, it only registers 10-11 volts, and it doesnt charge the battery. I was starting to thing that it was just running off the battery because when I pull the cable off the positive side, it kills the truck, but when its running, it keeps a constant voltage, even though its low. Only other thing I can think of is the voltage regulator, but I'm not sure (not used to working with this external regulator setup. Any ideas?

First have your battery load tested nd charge or repace as neede. Not good to take a battery cable off when engine is running; you may have fried your alt. Charge line should be hot all time. That is the wire held to the alt with a nut. 2 wires at voltage reg are red and green. Red should be hot with ignition on. Green is return from alt and is used by the voltage to control rate of charge. You can remove the connector from the regulator and temp ground it with ajumper wire ( full field the alt) and the alt should produce max charge. Female pins in this connector can spread causing a bad connection. Check that and post back.