cat 924F electrical problem

I have a CAT 924F that blows the 1st fuse on the left hand side of control panel ; it has the battery symbol above it. the wire coming out of the fuse is a yellow wire with the number 120 printed on it. The fuse blows immediately upon turning the key on. I would like to know what is on this circuit and where this wire goes to in the harness. Would appreciate any wiring diagrams anyone might have. Thanks, Terry