Installing Factory gauges in a '71-'73 Mustang

[Mach 1 Club]

By Rich Pajzer
Edited by Steve LaRiviere

Tachometer
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 connector that goes on the back of this one, as it's different
than the connector that will be in the car now.

Cut off the old wire connector, and solder the new connector 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 doesn'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
properly.


Ammeter

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.

[Mister 4x4]

Nice write-up.

Something else to consider - my instrument cluster came with a clock/speedo configuration, instead of the warning lights/speedo or tach/speedo configuration.  Since my center console came with a factory clock, I decided to swap the cluster clock for a tach, but wanted a factory look.  I went to Rocketman's Classic Cougar Innovations and purchased a factory clock-to-tach conversion.  The tach installs like an aftermarket tach, so no cutting into the factory harness or circuit board (which couldn't possibly work since the non-tach cars don't have tach wiring anyway).  

Here's my factory clock/speedo configuration (complete with non-working clock movement, cloudy factory 'glass,' and old car smell):


As the 'surgery' began.  Simple matter of disassembling the cluster and removing the clock from the unit (I also replaced the factory 'glass' and cluster printed circuit with new repop units from Ohio Mustang Supply):


Easy enough to swap and reinstall.  I ran separate wiring for the tach according to standard aftermarket tach installation instructions, but used some bullet connectors for the ability to disconnect and remove the cluster if necessary, along with color coded wiring (red, black, and green).  The tach works like a champ and looks close enough to factory as well: 


While I was at it, I replaced the factory ammeter with a voltmeter.  Factory ammeters can be problematic in the way of a dead battery and could potentially cause a fire, since they're attached to constant power source - they're always on, in other words.  The wiring, gauge, and voltage regulator need to be in tip-top working condition to avoid issues.

The only available downward sweeping voltmeter I could find was a Bosch unit from Summit Racing.  Basically, you remove the gauge internals from the housing and swap into the 3-gauge assembly - no modifications to the factory unit are necessary (no cutting or anything of that nature - just pretty much demolishing the Bosch housing to get at the gauge face and internals).  Wire it up separately as well, since the yellow ammeter wire is constant hot from the battery - disconnect it from the battery end (from the voltmeter harness, I believe) and remove altogether for a cleaner appearance.



Works awesome and doesn't draw the eye to an upward sweeping gauge sticking out like a sore thumb between the other two factory gauges:


As seen in the picture above, I also swapped the factory 'peanut bulb' dash lights for LED units.  For best results, you need to remove the blue diffusers on the gauge assemblies (which are now brittle and allow very little light to pass) and ensure the LEDs are installed correctly according to socket polarity.  The blue diffusers, combined with the yellow incandescent light from the factory bulbs would create a green hue for the dash lights - many different colors are available (including factory 'green'), but I went with basic white for maximum brightness.  Leave a factory bulb in the circuit somewhere, and the dimmer function will work as well (I like my dash lights bright and clearly readable, so I could care less about the dimming feature).


My ONLY regret is not making a 'VOLTS' label for the voltmeter for consistency sake, because this is what's involved for one wanting to make the swap:

[JTS71 Mach1]

Excellent Job, fortunately the Mach1 / Mustang dash comes apart in several pieces, and you can do a lot. Some cars the entire dash must be removed to accomplish any extensive work. Like my Jag/ Jacobra, the whole damn thing has to come out. From what I can find out, it's about an 8 hour job! Yuck.

JTS

[Mach 1 Club]

Great thread! That's always what this sites been about is information :)
Are those center gauges still sold?

I'm still in the mechanical mode with my 70. Just put in a new tranny, all new power steering restored, now it needs suspension and brakes. Then I hope to drive it to see what the motor needs immediately. Then save for a new motor :)
I'm just trying to get mine drivable.

You guys are amazing diehards. thxs!

[Mister 4x4]

https://www.summitracing.com/parts/bgs-f.../overview/

Sorry for not replying sooner - I kinda lost track of this thread.

Yes, Summit Racing still sells the Bosch downward sweeping voltage gauges.