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Discussion Starter #1
I'm trying to get my stock tach to work with an MSD 6A box & MSD coil. I know the tach is a "pass through" type of tach that goes inline with the coil + wire, but when I put it in line between the MSD box and the coil, my tach reads 3500RPM at idle. Any suggestions on how to make this work?
 

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Discussion Starter #3
Did you bypass your resistive wire when you installed the msd box.
I didn't see a ballast resistor wire ; it's apparently long gone. The stock tach was completely disconnected when I got the car.

It's my understanding the resistor was there just to make sure the stock coil only ran @ 9V during operation. Even if it were in place, since the coil is being ran by the MSD box, the ballast resistor's not even an issue?


***EDIT***
I hooked an autometer street tach up to the coil + wire and it reads as it should, so it's not a signal issue.
 

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Discussion Starter #4
Moved the tach's ignition side from the coil wire to the ignition switch. It shorts out if it's direct, but if I put a 22ohm, 10W resistor inline, the tach works - sort of. It hangs some, but I think if I play with the value some (or find a ballast resistor), it'll work.
 

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The Mustang has a resistive wire from the ignition to the coil. When you connect a stock tach you are going thru this wire. I suspect if you bypass this wire as they often do with aftermarket ign systems you will be running a higher current thru your tach.

If you are using a aftermarket tach, This would not apply.
 

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Call MSD support line there is a resistor that you need I think its part # 8910 or something like that. its about 30 bucks and summitracing carries it in stock, but they will tell you the correct part number.
 

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Discussion Starter #7
Call MSD support line there is a resistor that you need I think its part # 8910 or something like that. its about 30 bucks and summitracing carries it in stock, but they will tell you the correct part number.

The correct tach adapter is part number 8920. I tried every way in the world to get around having to use one, but it looks like I don't have a choice.
 
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