Engine swap starter problem?

Help please!
I just replaced the engine in my 97 Silverado 4x4 and every time I hook up the batteries the engine turns over. I can't imagine what I did that would cause this. I have every thing connected except the spark plugs are out. It was suggested that the engine be turned over without them in before starting for the first time. Any help with this would be most apprecieated. Thank you, Mitch

I pulled the starter out after work last night and tested it. It was working so I put it back in and now it works.