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Tach. installation. 1971 Mustang

8701 Views 5 Replies 6 Participants Last post by  Thank God
Hello, thanks for the warm welcome. My question is: I have a 1971 Mustang in which I'm modifying the instrument pannel to a Mach 1, I have so far done the central instrument cluster and about to install a original used Tach. My question is how do I go abut wiring it. The tach. has only to black wires coming out of the back. Which goes to the ignition switch and which to the ignition coil?
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Welcome... We'll find you an answer in here.
Those tachs can be seried through the coil to make them work. They are not like newer electronic coils that have switched power and a coil feed. Try seriesing the tach trrough the - side of the coil leads or + side , it will work that way.
Installing Factory gauges in a '71-'73 Mustang

Here's a good write-up from the 429 Megasite​

To install the Tach in a car that didn't come with them, first purchase a used
speedometer/tachometer assembly.

You will need the wire connecter that goes on the back of this one, as it's
different than the connecter that will be in the car now.

Cut off the old wire connecter, and solder the new connecter in place by
matching the color codes of the wires. You will have a few wires left over,
just tape them up, they were for the idiot {warning} lights.

Next, at the fuse block, locate the red wire w/light green stripe and tap into
it with a wire. Run this wire to the male prong on the tach.

At the ignition switch, you will find two red wires w/light green stripes that
are together.

Cut both of them. One of these wires runs to the positive side of the coil. This" Coil Wire" is the wire you want to locate. You will need to use an ohm-meter to check for continuity to the positive coil wire to find out the correct r/g wire to use. Once you have the correct wire, connect this to the female prong on the tach. (This "correct wire" is the "Resistance Wire".) Solder the other cut r/g wire back to the ignition switch where it was cut. That's it!

P.S. If the car dosn't run, it could mean that the Tach was bad, as the power to the coil has to go through the tach, before it reaches the coil. If this happens, just un-plug the Tach, and jump the two wires together so that the car will run.

{Also on the tach where I say to cut the 2 wires, and then use an ohm-meter to locate the correct wire... you really don't need to use the meter. All you need to do is have the car running...cut each of the 2 wires , one at a time ,until the car dies. When the car dies, you have located the correct wire. Connect the other cut wire, if it was already cut. (This should be easier, if someone dosen't have an ohm-meter)

Oil Pressure and Water Temperature Gauges
To hook up the stock gauges, first connect a 'D' size battery to the gauge to
test it. Try it in both directions until the gauge works correctly. At this
point mark the gauge with a plus and a minus, to correspond with the correct battery hook up.

Next, purchase the correct gauge sending unit from a parts store, and install
it in place of the oil light sending unit. Next, run a wire from the + stud on
the oil gauge to the stud on the fuel gauge. This fuel gauge stud must be the
stud that faces the left (drivers) side of the car when the fuel gauge is
installed, not the right hand stud. You can use a connector that's similar to
the type used on the ignition coil or starter solenoid, for this connection.

Next, at the speedometer cluster wire connector, locate the white wire w/red stripe. Cut this wire near the connector. Tape up the end closest to the connector, and run the other end, the - on the gauge.

Test, and mark, this gauge in the same manner as the oil gauge. Now remove the temp light switch, and add the proper temperature gauge sending unit in it's place.

Next, connect a wire from both the pluses on the oil and the temp gauge.
These will be connected together.

Next, locate the red wire w/white stripe at the speedo cluster connector, and cut it. Tape up the end closest to the connector.

Take the other end of this wire and connect it to the minus on the Temp Gauge.

Next, at the ignition switch, locate the red wire w/white stripe and cut it.
Tape up both ends of this wire, as it's not needed now. This was the wire that turned on the temp light during cranking. The gauge will work better without it.

Solder all your connections, as the gauges need tight connections to work

There are two ways to install the ammeter.
One way uses the "Junction Block", and the two heavy cables that are connected to it. This block was only used on cars that originally came with the gauges. It was located to the left of the voltage regulator. Also, some wires will need to be cut from a car that originally came with the ammeter, and spliced into the harness of the car that the gauge is being added to. This will make everything look "stock" under the hood.

Here is the way to add the stock ammeter to a car that didn't come with one.

This method looks "stock", when you're finished. Take this one real slow. Check the gauge in the same manner as the others. The needle will move real fast during the test, so watch it closely. Disconnect the car battery. You will need to add the "junction Block" from a car that came with gauges. The "block" is mounted to the left of the voltage regulator. Next, remove the heavy black wire w/orange stripe from the battery side of the starter solenoid, and install it to the "block".

Next, remove the yellow fuseable link wire from the starter solenoid. Follow
this "link" down around 8-10 inches. At this point you should come to a large splice joint in the wire. Two inches AFTER this joint, you need to cut this yellow wire. Save the link. Next, you need to cut a one foot length of the black/orange wire from a parts car. Make sure it still has the eyelet on it. Next, cut out the other black/orange piece of wire, (this one doesn't need the eyelet.)
This can also be cut from an old parts car. Now, follow closely. Lay the
black/orange wire down in front of you so that it's running horizontally with
the EYELET to the right. Tape this all down to hold it.

Half way in the middle of this wire, solder in the other heavy gauge wire that
you got. Hold it vertically so that it forms the bottom of the letter 'T'

Label this added wire as "A". All your wires should now look like the letter T.
Label the wire on the left of the T as "B". Where the T joins together in the
middle, add a small wire. Five inches to the left of this ,add another small
wire in the middle of the "B" wire. Solder the saved Fuse Link to the end of
the "B" wire. Connect the eyelet of the heavy black wire to the "junction"
block. Connect the eyelet of the fuse link to the battery side of the starter
solenoid. Solder the "A" wire to were the fuseable link used to be attached.
The two small remaining wires need to be run to the ammeter, by following the harness to the fire wall. Make a small hole in the fire wall grommet for the wires, and then add a dab of silicone to seal the hole.

If the needle moves in the wrong direction, reverse the connections to the
gauge. The gauge lights will be wired to the dash lights. Tape up all the
exposed wiring.
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Excellent piece. The only question I have is how about if you have an msd system like I have. All I need is the tach I've got the oil,amp,and temp gauges. Mine has the clock not the idiot lights will it work for me the same?
Nice write up!!!!!!!!!!!!!!!!!!!!!!!:bigthumbsup:bigthumbsup:bigthumbsup:bigthumbsup:bigthumbsup:bigthumbsup:bigthumbsup:bigthumbsup
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