Technical Sun Super Tach goes to 2500 max

I have a Sun Super Tach, worked great until today, now it only goes to 2500 rpm's max, any ideas?

 

Is it set on the right number of cylinders for your engine?

 

Its a fixed 8 cyl tach (no switch), worked perfect for a year.

 

Did you check all the wires? Maybe a bad ground.

 

Sounds to me also more than likely a weak ground .

 

What ignition system is it hooked to? Points, electronic? What coil?

 

Always check the easiest thing first. I agree with the suggestions that it's a weak ground........
or a break in the wire inside the insulation. Probably somebody's size 12 shoe stressing the wire under the dash or a pedal mashed it enough times. The tach has probably been around the block a few times and wire(s) may have been spliced, including inside the pot.
You could check the wire with a meter or just go straight to fabbing a new wire.

 

Maybe it's the engine...