[Mgs] Mode of failure for ignition coil

[Paul Hunt]

Ron - measure the primary resistance of the Moss coil, it should measure about
3 ohms.  If it measures about 1.5 ohms then it is a coil for a rubber bumper
MGB with 6v ballasted ignition system.  This will double the current in your
ignition system which could well affect the tach.  The other thing that can
affect the tachs fitted to 72 and earlier MGBs is if a Pertronix or similar
after-market electronic ignition system has been fitted.  But simply changing
the coil from one correct type to another correct type shouldn't cause that to
come and go, unless possibly the original coil is going high-resistance which
may damp the effects of the Pertronix, so measure your original coil as well
out of interest.

PaulH.
  ----- Original Message -----
  I have a question about the coil on my 66MGB.  After a recent rebuild of the
  engine I installed a new "stock" coil purchased from Moss.  I immediately
  noticed that my electric tack started jumping all over the place when the
  RPMs got over 2000.