Hey guys, tach issue here. I’ve got 12v to the coil, also good continuity on the yellow and green wire to cluster.
Cluster seems to work, even clock ‘tries’ to work.
Is there a ground somewhere I’ve overlooked, or any way to test tach?
Just now getting close to starting engine after 2 year restore so don’t know if it’ll show RPMs but shows nothing when key on ACC.

 

The trailing coil drives the tach. Do you show battery voltage with key at acc? Verify good ground at left shock tower then engine. How it switches is still a mystery to me Have you downloaded the wiring diagram and FSM yet?

 

Doesn’t show battery voltage at acc. I’ll check grounds. Thus far I’m using Haynes manual, I’ll download the factory as well.

 

Not specific to the tach, but what is the vintage of your battery cables?? These do NOT last 40+ years of reliable use. And poor ones, which my 'look fine' can be a niggly source of power issues. If you do not have a record of replacement, this is a good start...

Stu A
80GS (yep, new cables...)
AZ

 

All cables brand new.

 

On SA's the leading coil is actually what drives the tach, at least from the factory. Reason being is that with the early smog system, in order to keep the thermal reactor hot enough the ignition system will sometimes switch off the trailing coil in order to allow more unburnt fuel into the exhaust to maintain the heat in the thermal reactor (it's a backwards sounding system, but I guess it worked). Perhaps if the tach signal is presently on the trailing coil it's not working simply because the trailing system is disabled (typically happens on start up and decel, as well as some other cases as mentioned in the fsm). For the FB they removed the part-time trailing system upon the replacement of the thermal reactor with catalytic converters, and at the same time moved the tach signal to the trailing coil.

 

Thanks, Ben for correcting my error. When Mike Malone was helping me get my SA running and systems working, the tach was one that was not working - battery voltage - only he had me verify the trailing coil connection. I've not seen it documented.
Clyde