I helped a friend of mine with a similar problem on his crane several years ago. He also replaced the alternator without checking the voltage regulator. Then replaced the voltage regulator when things still didn't work. After 3 alternators and 2 regulators he was still not willing to listen to the idea that something was shorting both components and he needed to replace several sections of rotted wiring and both components at the same time.
He took it to an electrical specialty shop where they were happy to replace several feet of wiring and install a newer Chevy alternator with internal voltage regulator for several hundred dollars. I was glad to learn from his experience on that one.
Bottom line is check the whole system out before putting in any more components to avoid frying the new stuff.
