I think the RPM gauge gets its signal from the alternator. Since you have charging issue also it sounds like the alternator or its wiring is worth taking a look at.
The hydraulic cooler is fed from the one fuse that supplies power to all the electrical gear on the backhoe platform. Unfortunately the wiring diagram does not show this wiring as it appears to have been added on after the factory. The electrical diagnosis section has pretty good detail on the wiring in this area so just follow the diagnostics . Note that the cooling fans on the cooler are known issues, they were installed with the hole for the wiring facing upwards. The rubber grommets degrade with sunlight and water leaks in the motor and rots it out from the inside. Make sure you can spin the blades by hand. If the other accessories like the rear lights or power tool hydraulics are not working than the fuse is probably blown. From memory if you have the hood off look at the fuse panel on the right side. The rear accessory fuse is all the way to the left. Its a red higher amp fuse than the rest of them. Note the cooling fans only run when the fluid is hot if you are running the backhoe for a long time. What can happen is you change the fuse and use the backhoe and at some point the fan tries to come on and burns the fuse. Odds are the fan is shorted out and when the fluid get warm enough to close the thermal switch, the fuse blows. Expedition Imports has the entire cooler assembly but I have not heard of source of a fan only. I just made an adaptor plate and bought some 24 volt truck cooling fans in their place.
