Power antenna question

I replaced the power antenna mast assembly, with nylon geared cable. Old antenna came out OK. Inserted new assembly, but it does not work right. It rolls down a bit and stops. When it is supposed to go up, same thing. Did anyone play with this? What triggers motor to stop pulling or pushing the antenna up or down? That seems to be the problem, looks like it does not know when to stop going. It is on a 95 Mystique.

If the old antenna gear was broken, there could be some of the old one inside. Take the nut off the center, and you will see a reel there. Also, it's tricky to engage the new antenna. I had a stripped internal gear in mine, I bought a new $30 antenna from antennax.com and took it apart, used the gears to fix the Ford, it happened to be a close match inside. You could try a used antenna from ebay, the clue is: is the rod down. Partial extension may mean stripped gears.