any ideas?

my buddy bought an 87 thunderbird, V6 auto. he bought it cheap cause it had a bad tranny, so his dad put a new tranny it in. he's a pretty good mechanic so i cant imagine he overlooked anything while installing it. But it wont turn over, the dash lights up when you turn the key on, but it wont turn over. he can jump the starter relay and get it to start. He put a new ignition switch in it and still no luck.

anyone have any ideas, or run into this problem before? i'm a chevy guy so this isn't really my area. thanks

replace the relay.