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?
1967 fastback ; Stock tach + MSD 6A?
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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.
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.
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.
If you are using a aftermarket tach, This would not apply.
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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