Camera guy

Hey everyone, first time posting. two questions I need help with. First one is I have a night owl dvr and I don’t have the original cameras with it. Have lorex cameras and some others and none work with it. how do I know if it’s the cameras or the dvr not working? How do I know which cameras would work with it if it’s not the cameras? second question. I previously bought a lorex system and love the cameras, but squirrels have chewed off the pigtail ends and I have several cameras that won’t work when I try to put new pigtails on them. The cameras only have a red and a yellow wire coming out of them and most pigtails have extra wires. I’ve hooked it up all kinds of ways and tested it but it won’t come on( like 5 of them are the same. Also tried and tried to research what to do. I assume I need those two wires to go into a board of some kind but I can’t find anything on it. I think I previously wired them to the chewed off pigtail and it worked but now they are all chewed off below the board piece that split the wires. im really frustrated and could use some advice. I’d really like to fix the Lorex ones because they are so much better. please help.