Why does my new alternator have 4 posts, not three?

yellow68runner said
From my experience,that ground was used when that alt. was used on the front wheel drive cars like the Omni,Horizon,Reliants etc. =P~

true that,
the 2.2/2.5 eng family ("k" platform) use rubber bushing inserts in the alt mounting bracket.

as stated though, there is no such thing as "ground overkill". I would
add the extra ground.