On the oil pressure sender, is there only a single prong out the end of it that connects back into the wiring harness?? I can't tell on mine if there used to be another one or not, it looks like there might have been but wanted to make sure before I put the engine back in.

I looked on Mazdatrix.com and this is the only picture I could find, and it looks like there is only one. I may be mistaken though.

 

correct, only one