On my 79 sa I was taking it around the neighborhood after tuning the carb a little and the tach was working. About 1/10 of a mile down the road it dropped to 0, but the car was still running. The voltage meter on the tach still works.

Where about should I start looking for the connections? Transmission or engine? I was under the car mounting some exhaust piping last night. Could I have bumped something loose or severed a wire? I'm about to look in the 85 fb FSM, but I figured they're probably different so I'd ask here in the mean time.

 

if you have the points still, the leading ignition stopped

 

mine did this when the alternator died - check the ignition system too.

When the alternator is dying, the gauge thinks the engine isnt on and the tach goes into voltmeter mode (ever notice that the tach reads voltage if ignition is 'on' and engine isnt started)

Note: on the 79, your alternator has a voltage regulator. its a lot cheaper than the alternator, so replace that first....

 

The tach lead on the 79's & 80's just plugs onto one of the coil connectors. Not too hard to knock it loose, but then you'd lose the voltage measure, too, I believe.

 

Alternator is brand new, still has the sticker on it.

What are the black bullet connectors for on the distributor?

 

What do you mean by points? By stopped, you mean the leading spark is not firing? The car wouldn't even start if that was the case right?