Cranks over briefly

Make sure battery has a full charge and all connections good, not just at the battery, all ends. At the starter motor, two voltage circuits, one should come from battery, hot all the time. The other circuit should go hot when relay is energized. There two sides to relay, the switch side, right side in diagram. Then the control side, left side in diagram. The control side needs voltage and ground to energize the relay. For testing you could unplug the relay, use jumper wire between terminal sockets, switch side, The top wire on switch side is fuse protected and hot all the time, I believe. If you try the jumper wire, make sure tranny is in park or neutral and parking brake is set. It should crank the engine. Now if you think the starter motor itself has a problem, you could remove it, lay it on the ground, hook up jumper cables properly from charged battery to starter, voltage and ground, at the least, it should kick out the drive gear and spin. If it won't even do that, something wrong. Some of the national brand auto stores will test the starter for you, if you take it to them.