What alternator is fitted - 18ACR? Please also clarify 'spade terminal', do you mean a fork or a 0.250 push-on aka Lucar receptacle.
On an ACR / A127 / A133 the 3-pin connector has two large blades for B+ and a small one for D+ / IND. Normally these are both output terminals connected to the main rectifier, but some versions use one as a battery remote sensing input.
There are various versions of the 14TR regulator fitted to ACR-series units with different voltage sensing arrangements. Some sense the D+ / IND connection only via the yellow lead, some have a red lead that connects to the rectifier B+ terminal to sense via the main rectifier instead of the field rectifier, and some have a further white lead for remote sensing at the battery terminals, with the option of inserting a battery temp sensor in series. This lead is terminated in a non-standard Lucar or ring according to version and officially called 'S' but I have seen an aftermarket unit marked 'B+'. On units with one of the blades in the 3-pin reserved for sensing, the S lead goes to the isolated rectifier plate, otherwise it goes to a separate Lucar blade mounted on the brush box. ISTR 14TRs with an S-lead won't work with it disconnected. I am not sure whether any of the above applies to the 19TR too, it's a long time since I saw one of those!
If any of this seems to apply to your alternator, post pics with the cover off and we can say which lead goes where. If no sensing wire exists in the loom a 4-terminal reg can still be used by connecting the sensing lead to the main B+ terminal.
As for 'frying' alternators, as their output current is self-limiting the most usual cause is bad continuity of the output cable causing transients or inadequate cooling. It would be interesting to know in what what they are 'fried' - rectifier, windings etc.
**Edited as I remembered more info**
