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Discussion Starter #1
Have an original 1966 w/289. Need help with new HEI distributor. New HEI has a pigtail with a red and a green wire. Green wire is supposed to be for the tach. Having trouble figuring out where this connects. Car has a factory tach. There is one wire coming out of the old distributor which connects to the negative side of the coil. Since the old coil gets discarded, where does the red and green wire from the new HEI pigtail go? I thought the red wire connected to the old red wire that ran to the positive side of the coil. If that is correct where does the green wire go? Thanks
 

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What do the instructions say? If it says the green wire is for the tach then that is what you do. The factory tach wire would have been connected to the neg side of the coil with the stock ignition. I would assume the red wire is switched power this came be connected to the wire that was on the plus side of the coil. If your original ignition had a ballast resistor or resistor wire feeding the coil you will want to find a different switched 12v for the red wire.
 

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Discussion Starter #3
Yes, they way I understand it the the tach runs to the negative side of the coil. Makes sense the black wire coming OUT of the distributor goes to the negative side of the coil. Problem is, there is no wire coming into the distributor from the tach and there is no wire running from the tach to the coil. Again the way I understand it there MUST be a wire running from the tach to either the coil or the distributor.

The instructions say red wire from the pigtail goes to switched power and the green wire connects to the tach. My questions are:
1) Is it ok to connect the positive wire from the pigtail to the positive wire that WAS connected to the old coil?
2) Considering what I said above, where should I be looking at for the tach wire that is connected to the motor? Or am I gonna have to trace the wiring from the tach which I really didn't want to do?

Thanks
 

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Have an original 1966 w/289. Need help with new HEI distributor. New HEI has a pigtail with a red and a green wire. Green wire is supposed to be for the tach. Having trouble figuring out where this connects. Car has a factory tach. There is one wire coming out of the old distributor which connects to the negative side of the coil. Since the old coil gets discarded, where does the red and green wire from the new HEI pigtail go? I thought the red wire connected to the old red wire that ran to the positive side of the coil. If that is correct where does the green wire go? Thanks
When you state "factory tach" are you meaning Rally Pac? If so, triggering is very specific as it's "current sensing" vs. voltage sensing used in the later tachs beginning in the early 70s.
 

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Discussion Starter #5
Yes Rally Pack. When you say current sensing as opposed to voltage sensing, please explain. Help me understand.

Thank you
 

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Yes Rally Pack. When you say current sensing as opposed to voltage sensing, please explain. Help me understand.

Thank you
There are two means in which to excite or trigger a tach. The Rally Pacs and other early tachs used "current sensing". In the early 70s manufacture moved to voltage sensing. Voltage sensing is more of what we're familiar with these days in adding a tach. The tach wire is connected to the positive terminal of the coil.
Current sensing, as it applies to Rally Pacs, has one of it's leads connected inline with the coil, so the current runs through the tach and onto the coil. Doing this, if that wire is broken,not only will the tach not work, but, the coil loses it's current source and the engine dies. One needs to know, if the Rally Pac is taken out of the circuit for repair etc., then a "'pig tail" must be inserted it's place for the reasons mentioned above.

Also, know if you choose to add "fancy" ignition like capacitive systems, you'll need adapters to allow the current sensing tachs to work with them. The good news, these days one can have their Rally Pacs and dash tachs upgraded with circuitry converting them to voltage sensing. This wasn't readily available when I was upgrading in the 90s.

There is much written on "current sensing vs. voltage sensing......hopefully others will chime in and add more details.
Hope this helps....
 

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BTW, in case you didn't pick up on it, there is no wire from the tach to the coil in your OEM tach circuitry. It get's back to how the R/P is wired into the circuit under the dash. You should research Rally Pac circuitry or chase down a copy of your years wiring diagrams. All good to have available for cases like these. You may not even need the green (tach lead) in your case.
 
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The HEI mod. has to have 12 volts to operate. I had to use a relay to get battery current to coil and mod. Current from ign. wire will not work correctly, but can be use to charge the relay for battery current to coil. If I knew more about your set-up that you are using maybe I could help more......
 

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I've never had a rally pack on my car only a vintage sun pro tach which is a lot easier to hook up to the HEI. I recently finished replacing the old summit custom harness the car came with for a 1965 OEM repro harness and after much thinking and questions asked i bought a second fuse box to power up my electric fan and HEI dizzy and this is the best thing you could do if you want to avoid butchering your old harness! This is the one i got from summitracing https://www.summitracing.com/parts/prf-70113/overview/ great quality and a breeze to install.



Jose
 
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