Topic: 1965-66 Rally Pac Tachometers

[Building 3]

I heard recently that with the Rally Pac, if the tach fails for any reason, and the car engine is running, it will stop because the ignition/coil circuit is wired through the tachometer. So a failure in the tach circuit shuts down the engine. Has anyone heard this, or is this just a myth?  Thanks.

[Brian Conway]

Myth.

[rocket289k]

I heard recently that with the Rally Pac, if the tach fails for any reason, and the car engine is running, it will stop because the ignition/coil circuit is wired through the tachometer. So a failure in the tach circuit shuts down the engine. Has anyone heard this, or is this just a myth?  Thanks.

That is correct - it is not a myth.  If you have a factory original Rally Pac (Faria style) the engine will shut off if the Rally Pac dies.  To be more specific, the tach consists of two fundamental parts: a transformer on the input side and a gauge on the output side.  If the transformer fails, then the gauge will read nothing and the signal to the coil will also fail and the engine will turn off.  This is because the Faria style OEM/NOS Rally Pac is wired in series with the ignition circuit.  Typically when an original Rally Pac dies it's due to the transformer failing.

Note:  There is an exception - gauge can fail but the transformer can still be operational and the car will run. 

PS - The reproduction Rally Pacs do not have this issue. 

Regards,


Ron

[Building 3]

Is there a way to wire around this? Do we know for how long Ford used this system of running the ignition system through the tach? It sounds like a reproduction tach is a better choice for a Concours Driven car.

[rocket289k]

Is there a way to wire around this? Do we know for how long Ford used this system of running the ignition system through the tach? It sounds like a reproduction tach is a better choice for a Concours Driven car.

I know places that will convert a NOS Rally Pac to a "3 wire setup" which eliminates this problem however that process effectively changes all of the internals of the tach (you may as well use a reproduction Rally Pac in that case instead of wrecking a NOS / OEM Rally Pac tach).  I use the NOS/OEM style tach in my car and I drive it everywhere - I don't trailer it.  If it were ever to fail it's just a matter of unplugging the tach from the ignition circuit and I'd be on my way (of course you'd need a screwdriver to remove the instrument panel screws get access to the wiring behind the dash).

So although the transformer in the tach can fail, I wouldn't view it as a such a liability that I wouldn't put a Faria style tach in a car. 

PS - I'm not aware of exactly when Ford moved away the Faria style tach to a Aircore movement.  I have to leave it to other to chime in.  However I believe it was well into the 70's.

Regards,

Ron

[J_Speegle]

I heard recently that with the Rally Pac, if the tach fails for any reason, and the car engine is running, it will stop because the ignition/coil circuit is wired through the tachometer. So a failure in the tach circuit shuts down the engine. Has anyone heard this, or is this just a myth?  Thanks.

Not always experience has shown me that it depends on why it failed (some electronic thing inside the mystery boxes

Have owned cars where the tach failed and the car would no longer start while another where the tach would work or not work intermediately and the car would always start

[CharlesTurner]

If the tach fails and car won't start, it's not that hard to re-route the resistor wire back to the ignition switch plug.

[midlife]

That is correct - it is not a myth.  If you have a factory original Rally Pac (Faria style) the engine will shut off if the Rally Pac dies.  To be more specific, the tach consists of two fundamental parts: a transformer on the input side and a gauge on the output side.  If the transformer fails, then the gauge will read nothing and the signal to the coil will also fail and the engine will turn off.  This is because the Faria style OEM/NOS Rally Pac is wired in series with the ignition circuit.  Typically when an original Rally Pac dies it's due to the transformer failing.

Note:  There is an exception - gauge can fail but the transformer can still be operational and the car will run. 

PS - The reproduction Rally Pacs do not have this issue. 

Regards,


Ron

Right on!  I have to explain this to my customers all the time; they still believe that any tach failure will cause the car not to run.  Or...if the car doesn't run, it must be the tach at fault!

[zray]

If the tach fails and car won't start, it's not that hard to re-route the resistor wire back to the ignition switch plug.

^^^^^^. Exactly.

 As far as alternate wiring to avoid ignition failure goes, don't bother trying some fancy wire-a-round. Tach failure of this type is not common enough to warrant the effort. Yes, it does happen, but infrequently, if not rarely. Your time is better spent elsewhere.

Z

[Building 3]

zray: Thanks for that info. It's reassuring to know that it is not a common problem.