Mine had the infamous
Black Copper Rot syndrome, where, over time, the copper wire leading from the batteries to the meter in the body has turned black through a process not fully understood by science.
Basically, the meter's receiving no power, and I'd bet a buck to a billion that's the cause. But I won't, so I'll simply recommend that tentatively.
If you can get it apart and are handy with a soldering iron, it should be no problem to fix.
It mightn't be
the problem, or even the only problem, but it's the best place to start before you start looking for spare resistors and winding coils for the meter.