Tach Problems

[Steve Brown <smbrown@annap.infi.net>]

Modified my tachometer on my '67 MGB to work on negative ground.  Now
it reads 4000RPM at idle and redlines with even the slightest increase
in real RPM.  Have I done something wrong in the rewire ( reversal of
leads on the "white wire loop" and reversal of resistor and lead to
voltage and ground points inside the tach)? or can or should this thing
be recalibrated?

        Thanks

Steve