My car is exhibiting symptoms of a bad coil (intermittent missing when hot
to the point where it stalls out, runs fine when it cools down.)
I put in a new coil (correct Moss part number) about two years ago when the
car had the same symptoms.
Everything that I am reading says that an 1980 model should use an
unballasted coil because the ballast resistor is in the wiring harness. All
of the wiring diagrams show two green and white wires going to the positive
terminal on the coil. Based on what I read, I would expect about 6 volts at
the positive coil terminal. My car has a single white wire on the positive
terminal. If I remove that wire and measure the voltage with the ignition
on, I get 12 volts at the connector. With the wire connected, ignition on,
I get about 11 volts at the positive coil terminal.
I have had the car since 1991 and it had 38k miles on it when I bought it so
I have reasonable confidence that wiring harness has not been modified. The
wiring to the coil looks original except where I connected a Pertronix
system two years ago.
I know that electronic ignition on the 1980 MGBs was different from what
they used on the earlier cars. Does that account for the differences that I
am seeing? Should I be using an ballasted coil?