My tach appears to read 50% of what it should. That is, when it reads 1000 rpm my outboard tach reads 2000 rpm. Interestingly, when the key is off the tach reads 1000. When the key is on it reads 0. I'm wondering if there are some things that I can check to see exactly what the problem is. If I need a new tach, has anyone rebuilt one? Steve Liggett