what small lug are you referring to? There's two unshielded connections on the starter. One, the big lug, will be connected to battery positive voltage which you verified. The second has a copper strap going to the starter itself. That will be zero if bad (goes to battery voltage when the solenoid is activated, you would hear a big click when the start button is pressed). There should be a small wire connected to a plug as well (at the arrow on the picture below). If you disconnect the plug and hit the start button, that wire should go to +12v when the starter button is pressed. Note that you might have to turn the X5 completely off and try a fresh start to see 12v - I would imagine it has a protection mode.



You can also use a 16 gauge or heavier wire to carefully jump the battery terminal to the spade terminal where that plug goes. It should activate the starter. It's the same procedure as this https://www.youtube.com/watch?v=GP6PbKhEzjU I do it while walnut blasting N54s.