Solar charge controller wiring
Some charge controllers have ways of programming the "LOAD" terminal, e.g. to only provide voltage at night (i.e. when there is no voltage on the solar panel). If you have voltage across the controller's BATTERY terminals but not across the LOAD terminals, that's something to look into.

You haven't really provided sufficient details or photos of the wiring to confirm that it's hooked up correctly, but it's not that complicated. However, I would advise you to mark the polarity on the wiring itself, just for safety (e.g. use red electrical tape to mark the positive wires and leave the negative ones black).