If your tranny is bolted to your engine, your tranny is grounded.

Are you certain that the ignition wire is attached at the same spot you tested the starter with? If it is, you need to have somebody get in the car and attempt to start the car while you're underneath it with a test light checking for current. There should be current through the ignition wire ONLY when the key is turned to start. If your test light doesn't come on, you've narrowed the problem to either the ignition housing or the wire. If your starter works, it's bolted to the tranny, it's connected to the battery, and there is current to the ignition circuit, it must work.