RJ's controller must come from a different part of China than mine. I have a LandStar 20a PWM controller (costs $39 locally including tax)
Instructions are very clear. The fuse must be on the pos line within 150 mm ( 6 ")of the battery on the controller-battery wire.
In addition, there must be a fuse on a controller-load wire (if used)but in this case it does not matter if the fuse is on the pos or neg wire according to the instructions.
Only thing is I can't find anywhere what size fuse it wants on the controller -battery line. It says total load line fusing (each load needs its own fuse) should not exceed load rating of controller.