I cant get my jeep to start? its an electrical issue.?

I just replaced my 4 cylinder engine with a straight 6 engine and would like to start it up before i put everything back together. I have all the wiring correct as far as i can tell. I only hooked up the essentials to start an engine and i cant get anything to happen. I turn the key to on and i get power to the dash and hazard lights but no head lights or turn signals. if i turn the key to start everything turns off and all i hear is a small click from a box mounted on the firewall. please help i've tried everything i can think of.