How do I fix my 1988 Nissan Pulsar?

How do I fix my 1988 Nissan Pulsar. I rebuilt the engine and it should run, but it won't start. My starter is new and it still won't turn over, but my lights and other accessories are getting power, the car just won't start. What could be the problem?, Could it be a relay switch from the starter, and where would that be?