Battery charger...which cable is positive / negative ?

Hi , I just bought a Schumacher Fleet multi- amp battery charger/starter from a friends wife ( friend has passed away,that's why im asking here) I know that he used it over the winter so it does work but the problem is that the red and black plastic/rubber boots that are on most charger clamp handles have fallen off and i don't know which one is positive or negative..there isn't a + or - where the cables go into the machine but i can see where the wires are crimped at the clamps and one has 3 wires and the other appears to be a single wire,any idea which one is pos and which one is neg ?? I dont have a volt meter to test them,was hoping discription of wires might tell someone in the know...thanks