Already confirmed glow plugs bad. Only one workingtake a closer look at the electrical diagram, something upsteam of the glowplugs is a more likely problem, glowplug relay? any fuses? poor wire connection? weak battery/connections? verify with a meter before jumping to a conclusion. I'm not sure, but I assume your gator should still crank but may be hard to start in the cold temps if ALL the glow plugs were failed.