72 - 79 Gauge Clusters and Wiring

My thanks to Spence, Dan, Rob, HR, Clark, and others for their inputs to this article.

If you see an area that needs expansion or if you have questions, PM or email through the site.

Part 1:

While they look similiar, there are a lot of differences in the '72 to '79 Gauge Groups that merits explanation. There are, in fact, 4 distinct groups of these clusters and there is a mixture of them between the model year cars. '72 and '73 are unique to those years, '74 and '75 are also unique to those years although some of these same clusters are found in '76 models. '76 "high" series was unique to the cars it was installed in, and '77 to '79 had some variations in those years as well. Be warned that when you purchase one of these for an upgrade or to replace your existing but deteriorating dash you may be in for some surprises.

These are the main groups:

Front:



Back:



These are the gauge covers for comparison, it should be noted that for some 1974 models depending on DSO code they did not have the "UNLEADED FUEL ONLY" branding on the fuel gauge, all US Market 1975 and up did.



The '72 and '73 Gauge Clusters used metal gauge face trim pieces and edge lighting to identify the gauge functions. This is the unique '72 and '73 Gauge Cover with associated pieces:

 

72 - 79 Gauge Clusters and Wiring (continued)

Part 2:

This photo shows the difference between the '72 and '73 Gauge Cover and the later year covers:



The case back where the gauges mount was modified beginning in 1974 and carried on through the 1979 models. Most of the differences are shown below:



One of the changes not readily apparent is the difference in the depth of the gauges, the change being implemented by increasing the size of the stand-offs cast into the back.



The printed circuit connectors and more importantly the pin outs were different for each of the main year groups:

 

72 - 79 Gauge Clusters and Wiring (continued)

Part 3:

6 different printed circuits were used across the groups. 4 of the six will be shown here, '77, '78 and '79 each had it's own engineering number on the circuit however, the wiring and pin outs appear to be the same.

'72 and '73 and the '74 and '75 printed circuits. Some 1976 models had the '74 and '75 cluster with printed circuit:



'76 and '77 - '79 Printed circuits: High series 1976 had a unique printed circuit that could also be found in some '77 - '79 series vehicles. This was dependent on options installed with these cars:



The gauge layouts differed between the year groups as well:



Tachometer and indicator lights differed through the year groups '72 - '76 Green Printed Circuit Tachometers are serial tachometers:

 

72 - 79 Gauge Clusters and Wiring (continued)

Part 4:

The '72 through '76 speedometers feature a 120 MPH range while the '77 - '79 featured an 85 MPH limit. Speedometers for the year groups:



Shown below is a Police 140 MPH speedometer fitted into a member's '77 - '79 Gauge cluster. Note no Trip Odometer.



Gauge Cluster wire harness on the back of the cluster differed between groups with the '72 and '73 using a harness that included one of the turn signal indicators in addtion to tachometer, ammeter, and clock wiring, shown below:



The '74 -'79 eliminated the need for turn signal indicator on the harness, and the '77 - '79 change the connector type and added a ground wire for the tachometer:



The '77 to '79 Tachometer changes from a serial tachometer. The wiring as shown in the picture above shows the three leads, connections for these tachometers is:
Red - power through ignition switch
Black - Ground G206
Green/white dots - signal from the (-) of the coil to the tach

 

72 - 79 Gauge Clusters and Wiring (continued)

Part 5:

Wiring:

This is the factory harness that connects the harness on the back of the cluster to the engine wiring harness:



This is the factory engine to fuse block harness that contains the integral tachometer and ammeter wiring:



For those that are troubleshooting Tachometer or ammeter wiring issues or those retrofitting a gauge cluster into a standard car the following rough sketches show the proper wiring paths:

1972 through 1976 (Green Printed Circuit) Tachometer:



Ammeter: To properly install the wiring for the ammeter you need an insulator junction block, one or two (recommended) 14 Gauge fusible links, 30-36 inches of yellow 10 gauge primary wire, and yellow and red 14 gauge primary wire (approximately 12' of each). Install the insulated junction block on the flat boss under the starter solenoid, take the original primary wiring off of the starter solenoid and attach to the insulated junction block, then install the shunt per the diagram below:



For those that are retrofitting a gauge cluster into a standard dash car you need to change the oil pressure switch with an oil pressure sending unit and then install the tachometer and ammeter wiring above. The final item required is to tap off of your cigar lighter power feed (light blue / white stripe) for clock power.

 

72 - 79 Gauge Clusters and Wiring (continued)

Part six:

This is the gauge harness pin-outs:





This is the standard cluster in the '72 and '73 (74 - 76 are similiar):

Front:



Back:



The Gauges and Optional clock:



It should be noted that the same printed circuit connector is used appropriate to the year groups, a '72 and '73 standard cluster would not be "plug and play" with a '74 and later cluster.

 

'77 thru '79 Tachometer Wiring (some '76)

This is a sketch of the parallel tach used in the '77 through '79 models and some '76 vehicles as well: