I have a 120M AWD grader that won't start. It started out with a bad battery (which I initially thought was the main issue). It would start, but it was hard to start, and then it completely stopped starting. I noticed that the fuel primer wasn't coming on when the switch was on, but here's the kicker—it would come on when the switch was turned off. I thought it might have been one of the ECMs, but my computer is reading all the ECMs correctly. I also considered the injection pump, but I'm getting maximum PSI from the pump. The solenoid on the injection pump is randomly engaging while the switch is in the 'on' position. I can't recall if that's supposed to happen, but the primer isn't coming on. I'm getting abnormal readings for RPM on my computer, and the tachometer jumps up and down, which makes me think it might be one of the speed sensors. However, I started to doubt that theory when I was messing around in the engine compartment, and the primer came on, the tachometer stopped jumping around, and the grader started running, but only for a few minutes. I couldn't get it to replicate that again, though. Nevertheless, all these symptoms, especially the tachometer jumping and the primer coming on when the switch is shut off, are still present.