1970 Mach 1 Hood tach
#11
Let us know if it works.
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#12
These guys on the site have been amazing in trying to help!

Thanks for the great help.

Let us know how it all works out and what you figure out.

We all love someone else's mystery.
[Image: Arizona_flag_32w.gif]
Southern Arizona
Current Mustangs:
1973 Mach 1

1971 Mustang Grande
1965 Mustang
[Image: stevenharris.jpg]
http://www.mexicomissionariesofcbt.blogspot.com/
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#13
(03-07-2018, 03:51 AM)Steven Harris Wrote: These guys on the site have been amazing in trying to help!

Thanks for the great help.

Let us know how it all works out and what you figure out.

We all love someone else's mystery.

Well, I have tried everything suggested but still the hood tach does not work. Running out of ideas other than somehow the hood tach is suddenly inoperative or broken.
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#14
If you've tried everything, including a new Tach Adapter, you are probably correct that the tach is inop.

Did you ever determine if the tach is voltage or current triggered?  If you don't know, did you try wiring it to the Tach Adapter for both methods?  These hood mounted tachs were dealer installed options, so who knows if they were current or voltage triggered.  Do you know how was it connected to the original ignition system?  Knowing that, would answer the current or voltage triggered question.  I truly doubt MSD tech support knows.  Most of those people are too young to be familiar with these older cars.
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#15
(03-07-2018, 08:10 AM)1969_Mach1 Wrote: If you've tried everything, including a new Tach Adapter, you are probably correct that the tach is inop.

Did you ever determine if the tach is voltage or current triggered?  If you don't know, did you try wiring it to the Tach Adapter for both methods?  These hood mounted tachs were dealer installed options, so who knows if they were current or voltage triggered.  Do you know how was it connected to the original ignition system?  Knowing that, would answer the current or voltage triggered question.  I truly doubt MSD tech support knows.  Most of those people are too young to be familiar with these older cars.
The tach was originally wired as such: green wire to negative coil side, red wire to positive coil side, black to ground, yellow to lights.
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#16
Wow!  That doesn't sound correct for either a current or voltage triggered tach.  With the green wire to the negative side of the coil I'm guessing it was a voltage triggered tach.  And the red wire to the positive side of the coil was merely a convenient power source.  But that power source only has 12V during cranking.  During run, it would be less than 12V since the power to the original coil went through a resistor wire reducing voltage to the coil and points.

Did you connect it to the MSD Tach Adapter as a voltage triggered tach?
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