As others have said because the tach drops sharply then presumably picks up
again with the engine it is LT electrical. A capacitor would have to go
short-circuit to cause this, and they rarely repair themselves, so I think
that is unlikely to be the cause. Likewise if the ignition switch goes
open-circuit momentarily that would also cause the ignition warning light to
glow brightly (as long as the momentum of the car is still spinning the
engine). If that's not happening (and the light normally works as the
factory intended) then ordinarily other than loose connections somewhere in
the white ignition switch to coil or black-white coil to points to earth
circuits older coils with riveted spades are a well-known cause of
intermittently cutting out. Later coils had threaded studs and nuts.
Replacement coil noted, and it could be premature failure of that. However
with a 79, and presumably American spec with electronic ignition, it could
also be the ballast wire, trigger under the cap for a 45DM4 distributor, or
additional components in and around the distributor for the earlier
trouble-prone 45DE4 distributor. Of course if you have some other kind of
ignition then it could be that.
PaulH.
----- Original Message -----
> Every once in a while, at highway speeds, our 79B cuts out just for a
> second or two and then runs fine thereafter. It always runs great except
> for this "glitch" every once in a while. When it happens the tach
> immediately drops off sharply and then almost instantly resumes normal
> operation. Any ideas?
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