The Tach Cluster - 1971-1973 Mustang
#1
How many times have you seen a Tach Instrument Cluster at a swap meet and thought that it would be nice to replace your base instrument cluster? You look further and find out that in order to perform this change you also need the unique wire harness that goes with it. Then you learn that the wire harness is either missing or too expensive. Anyway do you really want to tear your whole dash out to replace the wiring? Good news, now you can modify your existing base wiring to be used with the Tach Cluster.

As you know, when the Tach was put into the right center pod of the cluster it forced the temperature and fuel gauges to move to the two outer pods. Ford replaced the charge and oil pressure gauges with warning lights. All these changes can be summed up into 4 categories: 1) Pin-out changes in the connector on the back of the cluster. 2) Oil pressure indication, 3) Charge indication and 4) The tach connection.

Let's start with the charge indication. The amp gauge is basically a worthless instrument. How many times has it actually told you that your charging system was bad? The warning light is not much better because by design it can only tell you when the voltage regulator is not working. It does not indicate complete charging system performance. Also, to switch over to the warning light is a major rework of the dash wire harness as well as replacement of the short alternator harness. This information leads me to suggest that the charge indicator in the cluster can be deleted. An add on voltage gauge put in a hidden place is not only the easiest thing to do, it is also the best charge system indicator. So, what we will do is: not use the amp gauge wires at the back of the cluster, add an aftermarket voltage gauge (if desired) and leave the rest of the charge system untouched. If you're interested in all the details to wire in the warning light, write to us at the Registry if there is enough response, a future article may be done.

Now to the fun part. Just follow the step by step procedure in proper order to install your new in-dash tachometer. Please read it through first so you get the big picture before you start.
A. Disconnect battery: wiring work here, be safe.
B. Remove dash pad.
C. Remove instrument cluster.
D. Rewire instrument cluster connector per the following sequence. To remove the pins from the connector shell push in the tab on the metal terminal with a small jeweler type screw driver. [See sketch 1] Before reinstalling the terminals into the connector shell be sure to bend the tab back out so that it clicks when the terminal is fully pushed into the shell. Give a slight tug on the wire to make sure it won't come back out.
1. Pull out pin 15 - put into position 3.
2. Pull out pin 5 - put into position 15.
3. Pull out pin 17 - cut off 3 inches of wire with terminal attached. Tape the end of wire left in the harness [To be used in step 5].
4. Pull out pin 2 - put into position 17.
5. Pull out pin 12 - Splice the 3 inches of wire with the terminal from step 3 above onto this wire to form a Y connect. Put one leg of the Y into position 2. Put the other into position 5.
6. Pull out pin 6 - put into position 12.
7. Pull out pin 16 - put into position 10.
8. Pull out pin 4 - put into position 16.
9. Pull out pin 8 - put into position 4.
10. Pull out pin 7 - put into position 8.
11. Pull out pin 11. Set aside, to be used in step 14.
12. Pull out pin 14 - put into position 11.
13. Pull out pin 13 - put into position 14.
14. Get pin from step 11 - put into position 13, this is the set aside pin.

[Image: tach1a.jpg]

Sketch shows view looking into the connector from the terminal end, not the side where the wires enter.
E. Find the coil circuit wire in the dash harness. This is the soft, fat, pink wire that comes through the firewall at the upper center. Cut the wire at the fuse block on 70's or at the ignition switch on 69's. Splice a wire pigtail in at this point to connect with the Tach wire. (see sketch 2). Cut as close to the fuse block or ignition switch as possible. This type of connector pigtail can be found at most Radio Shack's, car stereo stores or auto part stores.
F. In the engine compartment, replace the large bell type oil pressure sender with the smaller pressure switch.

[Image: tach2a.jpg]

G. Remove the 3 wire harness [coil, temp, & oil] which runs near the driver side valve cover and measure the resistance of the oil pressure wire [center pin]. If it is original it should measure about 5 ohms. If it measures 0 ohms put it back on the car and go to the next step. If it measures 5 ohms, do one of the following two things: 1) replace with another harness that measures 0 ohms or 2) Un-tape the wires and splice in a new wire to bypass the length of resistance wire [black] and then retape. It should now measure 0 ohms. Reinstall it in the car.
H. Check the replacement Tach cluster flex circuit on the back to make sure there are no breaks. Repair as necessary. This is also a good time to do a general clean up of the whole cluster.
I. Install the Tach cluster in the dash.
J. Connect battery, start engine and test cluster.
K. Reinstall dash pad.
L. Install aftermarket voltage gauge per the manufacturer's instructions if desired.

And there you have it, your in-dash Tachometer!
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#2
Sounds like a good idea. The only reservation I would have is cutting the large pink wire, that wire is what ford uses for ballast resistance for the ignition system.

Maybe there is another way around it? Idea
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#3
Well this is what I was told could be done, Im going to run this idea by Dicks Speedo and see what they think, mostly when I find stuff on the net I try to snag it. The whole goal for this site is to have all information about Mach 1's in one place, Ive spent weeks looking for info for my car and it has been a dig!

Thanks for pointing out "cutting the large pink wire, that wire is what ford uses for ballast resistance for the ignition system."

I'm definitely not a genius with all this stuff so having someone like you around is definitely a bonus. Thanks for still coming around and don't be shy about spreading knowledge that I know you have!

You should also add some photos of your car. The whole goal here is to get people seeing others participating. I'm seeing a lot of traffic just no one really signing up.
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#4
Keep us updated if you are going to attempt this. I might try it in mine as well.
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#5
I will. Still trying to determine when to do this, also need to find a quality center console since Im going to lose idiot lights. Everything is just a cash flow problem right now for me. Thanks for coming around!
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#6
what year mustang is this for?
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#7
1971-1973 Mustang
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#8
thanks a lot Joe. i read some place in here how to to this but they said the first thing you need to do is find a wireharness with the tach and cut off the plug. so if i understand this correctly i use the same plug that is in the car that did NOT have a factory tach?
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#9
Although I added this article 08-22-2009, I did not write it.
Someone else is better to answer this question.

I personally was not going to do it this way. I had the tach and the complete wiring harness to go in my 1972 Mach 1.
During my research of changing mine out, I came across this article and thought it would give some "motor head" a direction.

I'm sorry I cant be more help. Sorry
Reply
#10
ok thanks
i think i will change the harness if i can find another one.i have one in my other car but dont want to strip it cause i plan to finish that one too. i have two complete 72's i want to do both of them but even if i decide ti sell the other one i want it to be complete to help out the next guy. i love these cars and dont want to see another one sent to a steel mill in china.
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