First, welcome to the forums. You will find a lot of help here. But you will help the helpers if you include sufficient and accurate information in your queries.
I believe you are referring to the MRC 501 powerpack, not a "Marc 501." If you are trying to wire a rerse section/loop or a turntable (which is one type of a reversing section) you are using the right parts. There is a wiring diagram at the link below that shows how to do the wiring:
http://1.bp.blogspot.com/-Z5f-7Lpp6I0/UVJgqCWMfVI/AAAAAAAACL0/MV3qlI25eKM/s1600/Dual-Cab-Control-Turn-Table.jpg
Good luck.
Need to this hobby and have some old equipment need help on getting the throttlepack to work with controller