I converted my 61 olds to and alt vs the generator. I used this method, using a new 2 wire alternator and new battery that is fully charged. The alt gets real hot after about 10 mins. If I unplug it, you can hear the load it was under stop, seems to be working hard. If you unhook the batt wire while running the gen ind light comes on as it should. By hot I mean you can't keep you hand on it.
I would say your internal voltage regulator is fried. You can get another one at Napa and take it apart, swap the part and be done in an hour or so. Not that big a deal to replace. You could verify it by seeing what your voltage is at ~2500 rpm. If you are over 14.5, that's your answer. Honestly, I get junk 12SI units, clean them up and replace the internals and they are fine. More power than I would ever need and I get to take them apart and clean and paint them to match the engine compartment.
are you sure the alternator in question is a internal self regulating one ?? as some of the older ones ( 5.5, 6.2 series pre 1973 ) are externally regulated and have plug ins on the unit like a 10si internal regulating unit (1973 and later) ,one way to tell the difference is the orientation of the terminals non Si's they are parallel like this and a si they are in line like this and a Si unit are inline like the one below and if you interchange them the non si unit will stay energized till you turn the key off . if its a 10si , more than likely the regulator like Diavolo said sorry about the large pictures as they were this size when I found them .
Okay, I had the alt tested and it is fine. I double checked all the wiring and its exactly like the illustration. Ready to put the generator back in.....
Only other thing I can think of is maybe you have the wires on #1 and #2 terminals reversed. I would unplug that connector and put a jumper wire from the alternator "bat" terminal and the #2 terminal. Start it up and see if it's still working hard. #2 is the voltage sensing terminal. For best operation it needs to be connected at the first connection where all the accessories get their power so it can sense the voltage drop as more accessories are turned on and increase output. Now.... If that voltage sensing wire happens to be hooked up correctly the way you have it wired, but maybe the wire has a break in it some place, which would make it 0 volts, the alternator would go to full output to try and compensate. So you could start it up and check your voltage at #2 terminal to see what system voltage the alternator is seeing.
I'm surprised it didn't blow the regulator by disconnecting the battery while running! These alternators need a load to regulate, and voltage usually goes sky high when the battery load is disconnected. I'd take the battery in and have it also checked. It may be the source of your problem. The alternator will run very hot if the battery was discharged, but once it's charged up the load should drop and the alternator should just run warm.
Before you get fancy...clip a jumper cable to battery ground cable at the battery and touch other end to alternator case. See if any drama results.
I've run a few other sbc/alts with no battery, no problems ever. You can tell the alt STOPS working hard when you pull the battery cable off.... Wouldn't it be grounded through the mounts?
It grounds to engine through mounts. From there on things get hazy...paint, especially good paint thicker than factory, gaskets, rubber in motor mounts, etc. all serve as potential barriers. Grounds are often taken for granted on both OEM and modified cars, but are often pretty bad!
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