Gaffrig Tach ????????

[DansBlown1973Nordic]

I have an electric tach in my V-Drive. The tach has worked perfect for three years. All the sudden the needle starting jumping around one day. Now it reads 8500 rpm,s wide open instead of the 6000 its always read. Could it be my MSD box is bad?
Can I hook my tach up to the my coil instead of the MSD box? Right now my tach feeds off a wire from the side of the MSD.

[502 JET]

If you are running an MSD box you MUST connect the tach to the box. If connected to the coil the tach may be damaged/not work.

[DansBlown1973Nordic]

Im hooked to the box. The first 10 or so hours the tach worked fine with the new box. Then all the sudden it went SCREWY!!!!!
I checked the selector to see if it was set on 8 cylinders. If I change to six or four will it read less or more rpm,s???? What are the A/B positions for????