Installing Factory gauges in a ’71-’73 Mustang

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 warning lights.

Next, at the fuse block, locate the red wire with 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 with 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 red/green 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 red/green 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 unplug the tach and jump the two wires together so that the car will run.

Also, on the tach where it says to cut the two 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 and cut each of the two 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 doesn’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 hookup. 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 plus stud on the oil gauge to the stud on the fuel gauge. This fuel gauge stud must be the stud that faces the left (driver’s) side of the car when the fuel gauge is installed, not the right-hand stud. You can use a connector 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 with red stripe and cut this wire near the connector. Tape up the end closest to the connector and run the other end to the minus 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 its place. Next, connect a wire from both the plus terminals on the oil and the temp gauge so they are connected together.

Next, locate the red wire with white stripe at the speedometer 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 with 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 with orange stripe from the battery side of the starter solenoid and install it to the block.

Next, remove the yellow fusible 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, making 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 down to hold it. Halfway in the middle of this wire, solder in the other heavy-gauge wire 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 where the fusible link used to be attached. The two small remaining wires need to be run to the ammeter by following the harness to the firewall. Make a small hole in the firewall 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.