There are generally 4 twelve volt circuits in Argosy's of that era. My best guess is that you don't have one (or more) of the 4 hooked up or fused. Since you are not using some other equipment or don't have it installed, you are not aware that those things are not working either, that is no 12 volts to them.
You will need to find the circuit end which supplies those lights in the front end of the trailer and connect it, through a fuse, to 12 volt
power. It is hard to help you further, as you have had the rig all apart and are putting it back together, and it is difficult to otherwise know what has been modified.