how do you know if you are over drawing your bow past your draw length?

If you are pulling with your arms, you can overdraw the bow and pull it way past your ear, if you have the strength and/or a weak enough bow.

If you are pulling with your back, it is virtually impossible to overdraw the bow, because you will run into a wall where your back muscles have contracted as much as they can contract, and your drawing shoulder blade has moved as close to your spine as it can move.  Your drawing arm is relaxed, and your elbow has described a J shape rather than a straight line.

So in order to avoid overdrawing your bow, you need to learn to draw with your back muscles.

any way to help with this to know you are doing this?

I believe you recently purchased Masters of the Barebow.  In volume 3, I believe, Rod Jenkins works with Darrel Quidort to demonstrate the Formaster.  The specific purpose of the Formaster is to help you to know you are using your back muscles.

Dave's advice, as always, is spot on. But I can't recommend enough, viewing Arne Moe's videos on YouTube. They will answer many of the questions regarding form that you have. Come to think of it, I need to get on him about making part 2, to that last video he made...

     
I hear you Sirius!!  Will see what I can do.

Arne

I think McDave's description is good.

I guess I think of it as your shoulders are fully expanded. The draw hand comes to your anchor whether it's some "side of the face" anchor or a more forward anchor like under the chin/Olympic style.

The only real difference being the angle from the string shoulder to the string elbow.

I don't really know what muscles take care of that part.