Possible wireing problem

I have a 1989 Mazda B2200 truck. Several months ago I removed the engine. A month or so went buy before I got a better engine put back in, then a few more months went by before I got around to connecting every thing. Now I am having some problems with getting the electrical correctly hooked up.I have searched and printed out every wireing diagram I could locate but none of them really give me a clear concise picture of what I need.
When I use a key (or a remote starter) to crank the engine it barely responds with maybe one or two slow rotations.
The battery is new, I have even tried with another battery to make sure. The starter is good and I am now at a loss at how to proceed.
What are the possible things I need to check? A fuse? A inline fuse? Wired wrong or incomplete?
What? Help please.
I know some will say to just junk it but the truck has sentimental value and would like to keep using it as a farm truck.
Thank you for any advice.