If you look at the second image with the wiring diagram, the red wire is in the wrong connector. The bottom connector will be for the black negative wire and the second terminal in is for the postive cable (Red). Now these are your supply from your van battery, so the eye lug will go on the positive battery terminal of your van battery. You will need a black cable for the negative cable which can either be put on the negative battery terminal or a earth terminal on the van body/chassis.
On the other side of the split charge relay you will have 3 connectors. All you are interested in is the bottom terminal with battery on it although the top one with fridge will work just as well. The 3rd terminal connector could be used as a small continual power source from the van battery, ie another internal light etc as that terminal will be live. (These split charge relays are for caravan users. The fridge terminal is exactly that; its the wire that goes to the fridge to keep it cold and will only work when the car's engine is running. The same applies to the battery as its for the caravan's leisure battery only to be charged when the engine of the tow vehicle is running. The light connector is for the internal caravan lights which you can use even when the tow vehicle's engine isn't running.) That cable goes to the postive terminal on your leisure battery. You then need to earth the negative terminal of you leisure battery with another black cable to the chassis/body of your van.
I would replace those clips with proper battery clamps if I were you. If you take the battery out to charge it, always make sure it goes back correctly and that you never start your engine with the battery out and the terminals lying around.
