.. how to wire a 3-pole starter relay ? ..

RE: you PM, don't know where you are located, or where you have been going for parts stores, but these relays were used from the early 60's until at LEAST into the 80's and maybe later.

They were used on ALL Mopar cars and pickups, and the 4 terminal ones were used on all automatic cars and trucks as well as "stick" cars starting in '70

Electrically, all 4 terminal relays are the same, only difference is mounting brackets.

With a good big soldering iron, you "could" convert the 3 terminal into a 4--just unsolder the ground at the corner, clean it up, and solder a male quick connnect on instead.