1970 Mach 1 Hood tach
#1
I have installed a new MSD 6AL ignition system and according to MSD needed a tach adapter. I have wired the tach adapter and tach per MSD instructions but the tach will not work. MSD hasn't been to much help. Does anyone know how to wire the 4 wires coming from the hood tach to the MSD system?
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#2
I had this set-up about 6 years ago on my car and my memory is failing to remember how I set it up.  Also, I don't remember what tachometer I used with it but it was definitely an older style one and it worked.  This may not answer your question but it may help in figuring out your problem:

INOPERATIVE TACHOMETERS

If your tachometer fails to operate with the MSD installed you may need an MSD Tach Adapter. Before getting an Adapter, try connecting your tachometer trigger wire to the Gray tach wire of the MSD. This output produces a 12 volt, square wave (see page 2). If the tach still does not operate, you will need a Tach Adapter. There are two Tach Adapters:

PN 8920: If you are using the Magnetic Pickup connector (Green and Violet wires) to trigger the MSD, you will need the PN 8920.

PN 8910: If your tachometer was triggered from the coil negative terminal (voltage trigger) and you are using the White wire to trigger the MSD you will need the PN 8910

Page 2: TACHOMETERS

The MSD Ignition features a Gray Tach Output wire that provides a trigger signal for tachometers, a shift light or other add-on rpm activated devices. The Tach Output wire produces a 12 volt square wave signal with a 22.5° duty cycle.


Also check this site out.  It seems to have some discussion on wiring the tachometer to the box:

http://1969stang.com/forum/index.php?/to...o-msd-6al/
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#3
I've been down that road with a factory tach.  Unfortunately they do not work with an MSD ignition box.  You will need an MSD Tach adapter.  MSD offers two tach adapters.  To determine which one you need, you will need to determine if your factory hood mounted tach is current triggered or voltage triggered.  If you are lucky, you will need the less expensive tach adapter.  The factory Ford in-dash tachs of this time period were current triggered.  I don't know about the hood mounted tachs.

Current Triggered Tachs:  The wire that triggered the tach was in series between the ignition switch and the positive side of the ignition coil.  Thus, power feeding the coil from the ignition switch went through the tach.  So sometimes when the tach stopped working the engine would also not run.

Voltage Triggered Tachs:  The wire that triggered the tach was simply connected to the negative side of the coil.

Either way, like I said, if you have functioning original factory tach and it will not work when connected to the tach terminal on the MSD box, you will need one of their Tach adapters.  The tach terminal on the MSD box is the only option to connect a tach.  Do not try connecting it to the ignition coil.
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#4
(02-21-2018, 02:16 PM)1969_Mach1 Wrote: I've been down that road with a factory tach.  Unfortunately they do not work with an MSD ignition box.  You will need an MSD Tach adapter.  MSD offers two tach adapters.  To determine which one you need, you will need to determine if your factory hood mounted tach is current triggered or voltage triggered.  If you are lucky, you will need the less expensive tach adapter.  The factory Ford in-dash tachs of this time period were current triggered.  I don't know about the hood mounted tachs.

Current Triggered Tachs:  The wire that triggered the tach was in series between the ignition switch and the positive side of the ignition coil.  Thus, power feeding the coil from the ignition switch went through the tach.  So sometimes when the tach stopped working the engine would also not run.

Voltage Triggered Tachs:  The wire that triggered the tach was simply connected to the negative side of the coil.

Either way, like I said, if you have functioning original factory tach and it will not work when connected to the tach terminal on the MSD box, you will need one of their Tach adapters.  The tach terminal on the MSD box is the only option to connect a tach.  Do not try connecting it to the ignition coil.

Mike - I believe he already has purchased a tach adaptor.  The issue may be the wrong tach adaptor for the application or it is not wired correctly.

The link I provide above seems to show some guidance on the wiring.
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#5
You are right.  My mistake.  Here is a link to the tach adapter I have always ended up needing this model with Ford original tachs.  Unfortunately it's the more expensive one.  It works with both voltage and current triggered tachs, stock points distributors and magnetic pick-up distributors like MSD and Ford Duraspark.  Still need to know if the hood mounted tach is current or voltage triggered when wiring it to the tach adapter.  There are also wiring instructions in that link.

https://www.summitracing.com/parts/msd-8920/overview/

FYI:  Unrelated to the tach issue, but sometimes overlooked when adding an MSD ignition box, is the original power wire to the coil is connected to the MSD box as the switched 12V power source.  The original power wire to the coil has a resister wire in it (instead of a ballast resistor) and should not be used for the MSD 12V switched power source.  Sometimes it will work fine, sometimes it will cause problems.
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#6
The 8920 is what I installed and wired it per instructions with MSD Tech Asst (wanted to make sure I did it correctly) It still doesn't work. The green wire was originally to the negative coil side, and the red was positive. Now per MSD the red is to the red wire from the adapter and the green is to the violet wire from the adapter.
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#7
In that case, before trying anything else,  I wouldn't hesitate to first exchange that Tach Adapter for another one of the same.  Those have a history of not being reliable.  If you purchased it from Summit Racing or Jegs returning it as defective won't be a problem.

Many years ago I needed the 8920 for use with an original 1969 Mustang in-dash factory tach.  Over the course of about 10 years I went through at least 5 of them.  It ranged from working for several years to a few weeks.  One didn't work from new.  It got to the point I purchased a spare.

Another option, but expensive, is those hood mounted tachs are being reproduced.  The more authentic looking versions sold through NPD are rather expensive.  Double check, but I believe they will connect directly to the MSD tach terminal.  If the new tachs are the current "air core" movement technology they will work much better than the original type.
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#8
Thanks for the info. I did purchase it from Summit and they have actually been more helpful than MSD has. If they are that unreliable I may check into a different option like you suggest, but may try a new adapter first. The tach worked fine before and you are right, the NPD tach is pricey. I'll see what I can do first to make it work again.
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#9
I've had excellent customer support from Summit Racing.  Only once, did they not accept a return.  It was for Scott Drake cast aluminum valve covers.  They were supposed to fit over roller rocker arms.  They hit both my rocker arms and near the bottom three bolts my valve springs.  I modified them trying to get them to fit is why I couldn't return them.  So instead, Summit gave me 30% off any other pair of valve covers I wanted.  I thought that was fair.

If you haven't called Summit with the issue and you still have the MSD packaging it came in, I'd suggest simply return it filling out the return label as defective.  Select the option to exchange it, or simply buy another one if you want if sooner.
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#10
(02-22-2018, 06:03 AM)1969_Mach1 Wrote: I've had excellent customer support from Summit Racing.  Only once, did they not accept a return.  It was for Scott Drake cast aluminum valve covers.  They were supposed to fit over roller rocker arms.  They hit both my rocker arms and near the bottom three bolts my valve springs.  I modified them trying to get them to fit is why I couldn't return them.  So instead, Summit gave me 30% off any other pair of valve covers I wanted.  I thought that was fair.

If you haven't called Summit with the issue and you still have the MSD packaging it came in, I'd suggest simply return it filling out the return label as defective.  Select the option to exchange it, or simply buy another one if you want if sooner.

MSD has now suggested that I move the negative wire that I had attached to a body ground to the negative side of the battery. Going to try that and see what happens.
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