M50 starter/starter wiring not working

[E30NS]

I have an M50 in my 318is, but it wont start unless i wiggle one of the black wires connected to the starter. There's 3 wires 2 black, and one red. Sometimes you just have to poke it, other times you have to wiggle it around a lot. When you do wiggle it around it starts great. I think its just a bad wire but im not sure. My battery is at a good 14v, well 12v now since i was trying to start it. The power windows sometimes have trouble going up and down, could it be the battery? How can i test if its the starter or the wiring?

[E30NS]

bump, someone help me!

[Gregs///M]

Remove the starter and check the studs are not loose mechanically. Also check the wires that lead to the starter. If those terminations are poor, dirty, corroded, oxidized, then you will need to correct that.

It sounds like you already know its the wiring so just take it apart and fix it.