I think it is very possible you could have another bad part from the parts store. I have seen weird symptoms caused by a bad battery. I don't know what the expected voltage reading is for the blue wire with key on. Somebody with more knowledge than me may need to chime in on that. A car parts store may be able to test all 3 parts involved, the battery, regulator, and alternator.
If you have some other problem not discovered yet and not related to those 3 parts, such as with wiring, then it probably won't fix it to upgrade. But if you are interested and want to proceed in that direction, it is probably a good idea anyway.
You can modify the wiring to accommodate an internally regulated alternator, or get an
adapter plug that bypasses the external regulator. Then just bolt in a new alternator.
This article describes and gives application information about the later model alternators such as 12SI.
http://www.madelectrical.com/electri...elcoremy.shtml
And this forum thread has lots of info:
http://67-72chevytrucks.com/vboard/s....php?p=8254922
That thread also has information about upgrading to the CS type alternators which are even later model than the 12SI, and CS alternators require a different connector and a resistor to be installed in one of the wires or another adapter. Some of the CS alternators require the pully to be changed out because some don't have a v-belt type pully. O'Reilly Auto Parts changed the pully for me in the store on the CS144 alternator I bought from them to go in my 1969 CST/10.