The motor is a Cummins. I assume its a 93 model. The tach is not working. I do not believe it is a ground issue because the guage jumps a bit when the key is turned on. All the other guages work. There is a lone bare wire coming out of a harness towards the front of the motor that looked like it would have extended down to the crankshaft balancer(it is short now with but similar debris wrapped around hub of fan). There is nothing down there that looks like a crank shaft position sensor. I did find at least one bolt that was loose on the front of the motor with oil pouring out of it. There are no charging problems. Question Does this motor have a cps? Is it located at the crankshaft balancer? If not, where is it located? Is it possible it came loose and now is gone, therefore not seeing it?
I never had an All Star, but did have the MVP-EF and several pushers all on Hendrickson/Thomas chassis. On all, the tach ran off of the alternator. There was a wire from the alternator just for that purpose. I'd check there first, make sure everything is tightly in place...that was usually my problem.
If this is an Oshkosh chassis, then somebody else will need to help!