Who knows without more info...
In the picture you show, there are 2 3/8" spades and 1 1/4" spade.
The 3/8" spades can be reversed so doesn't matter where it goes.
The 1/4" can only go it the upper most position.
The 3 spades note Field (1/4" spade), positive (1/4" spade), positive (3/8") spade.
Some have 2 3/8" spades like your picture.
Field wire that charges your field and creates the electrical field so your alternator produces positive current (and operates your red alternator warning light). This wire is brown with yellow stripe or yellow. The rest of the wires are brown.
Originally there was a 3 wire plug that prevented getting the 2 1/4" spades mixed up.
So you do not have a 1/4" positive plug and don't know which spade your field plugs into.
Going from memory the field spade plugs into the 1/4" spade on the end.
Leave it unplugged and switch on the key.
The alternator warning light will not glow.
Now plug it on the end and switch on the key.
The alternator light should glow.
start the engine and the alternator light should go out.
You got it.
If this doesn't happen as described above, then plug into the other terminal (that matches your spade size) and repeat the test.
Hope this helps
Uncle "Richard" Douglas has a Land Rover with big wheels that never gets stuck... until he breaks something so it won't go. Uncle Douglas always breaks something. - Anna Crowther at the Conclave 2012 (AKA Carburetor Neck)