Same here never have found a diagram tried to get one from M&H but got some storey about copy rights. I bench tested My Ammetter gauges work (test with a 9 volt battery and a POT) but it doesn't work connected to the harness, nothing is comming over the wires. This is a brand new wire harness throughout the car.

I think the way David connected his up is the same as the note I Gathered below from the Q&A section on this site. This next spring I will be tearing into it to see why it doesn't work and contacting M&H to see what they can tell me.


Pin # Wire Color Usage
1 BLUE/WHITE Stripe Oil Pressure Gauge
2 GREEN Water Temp Gauge
3 Light TAN Fuel Gauge
4 GRAY Illumination Lights
5 N/A
6 GRAY Illumination Lights
7 Light BLUE Left Turn Light
8 Dark TAN Brake Light
9 Medium BLUE Right Turn Light
10 PINK (2 wires) GROUND (see note below: +12VDC)
11 WHITE Volt Gauge
12 BLACK Volt Gauge


The BLACK and "BLACK with WHITE Stripe" wires are used for the ALT gauge. These two wires are of a heavier gauge than most of the wires in the forward lamp harness because they have the potential to carry higher current levels than either the TEMP sending unit or OIL sending unit wires. The "BLACK with WHITE Stripe" wire is connected to a one end of a "fuse link" near the voltage regulator. The other end of that same "fuse link" is connected into the "power distribution splice" via an even heavier gauge red wire. The power distribution splice is a group of four very heavy gauge red wires, (contained within the forward lamp wire harness"), which are soldered together very near the voltage regulator. This splice distributes the output of the alternator to the horn relay, voltage regulator, charging junction block near the battery, AND one side of the ALT gauge on the Rally Cluster. A "fuse link" is a wire, which is designed to "open up" should too much current pass through it. (Consider it a fuse in the form of a wire, which is easily identified by rubber-like insulators at both ends.) The BLACK wire is connected to one end of a "fuse link" near the junction block by the battery. The other end of the same "fuse link" is connected to junction block itself via a heavy gauge red wire. The "BLACK with WHITE Stripe" wire of the forward lamp harness gets connected to the WHITE wire of the Rally Gauge cluster connector, (pin 11). The BLACK wire of the forward lamp harness gets connected to the BLACK wire of the Rally Gauge connector, (pin 12).

By completing steps one through six, you now have successfully re-pinned your cluster connector to work with a Rally Gauge with the exception that the volt gauge will be inoperative if you stop at this point. To get the volt gauge operative, you will need to add two additional wires. Since the metal pins for the cluster connector are hard to come by, the following steps illustrate how to connect the volt gauge wire to the cluster, without going through the cluster connector. I recommend going to your local hardware store or home improvement store and picking up 20 feet of exterior grade, insulated, two conductor extension cord. This is the type of wire that is typically used in exterior grade extension cords. The covering is usually BLACK rubber and the conductors inside are BLACK and WHITE. Since this type of wire is designed to carry 120V, it is of sufficient gauge to handle the current flows of the Firebird's voltage gauge. Another bonus of using this type of wire is that the covering is NOT likely to rub off and cause a short. (The stock voltage gauge wires are heavy duty as well). You will also need to pick up a package of "round eyelet" type wire ends. You will need three. (You will use two of these to attach the wires to the back of the gauge cluster, and to attach one of the wire to the power junction block near the battery.) Also pick up a package of rubber grommets that have the interior diameter to match the wire. You will want to use a grommet where the wire goes through the firewall. On you way home from the hardware store, stop by your favorite auto parts store and pick up a couple of "orange" fuse links as well. Fuse links are rated by their color, and that is why I specified "orange".

Wiring the Volt Gauge Circuit

By completing steps one through six, you now have successfully re-pinned your cluster connector to work with a Rally Gauge with the exception that the volt gauge will be inoperative if you stop at this point. To get the volt gauge operative, you will need to add two additional wires. Since the metal pins for the cluster connector are hard to come by, the following steps illustrate how to connect the volt gauge wire to the cluster, without going through the cluster connector. I recommend going to your local hardware store or home improvement store and picking up 20 feet of exterior grade, insulated, two conductor extension cord. This is the type of wire that is typically used in exterior grade extension cords. The covering is usually BLACK rubber and the conductors inside are BLACK and WHITE. Since this type of wire is designed to carry 120V, it is of sufficient gauge to handle the current flows of the Firebird's voltage gauge. Another bonus of using this type of wire is that the covering is NOT likely to rub off and cause a short. (The stock voltage gauge wires are heavy duty as well). You will also need to pick up a package of "round eyelet" type wire ends. You will need three. (You will use two of these to attach the wires to the back of the gauge cluster, and to attach one of the wire to the power junction block near the battery.) Also pick up a package of rubber grommets that have the interior diameter to match the wire. You will want to use a grommet where the wire goes through the firewall. On you way home from the hardware store, stop by your favorite auto parts store and pick up a couple of "orange" fuse links as well. Fuse links are rated by their color, and that is why I specified "orange".

7 Terminating Volt Meter Circuit Wires at the Cluster

Step seven is where you want to attach the round wire ends to the BLACK and WHITE wires at one end of the extension cord. I recommend removing three inches of the exterior insulation. You can either solder or crimp these connectors on to the wires. Now looking at the back of the cluster, you will see two screws where the flexible circuit board attaches to the voltage gauge. Attach the WHITE wire to the left screw and the BLACK wire to the right screw. (This is where the round wire ends come in handy since there is no way the wire can come off unless the nut falls off. This makes a good solid connection.

8 Preparing the Firewall for the Volt Gauge Wires

Step eight is to find a suitable place, and drill a hole through the firewall for your new "wire harness". I recommend just above the fuse block. The size of the hole will be dictated by the "hole diameter" specification of the grommets you will use. Drill the hole, use a round file to smooth out the edges, and then install a grommet in the hole.

At this point, it is a good idea to reinstall the cluster in the dash. That way you will be able to see the best way to route the new wire from its permanent resting spot on the back of the cluster to the hole in the firewall.

9 Installing Volt Gauge Wires in Firewall

Step nine is to fish the wire through the opening in the firewall, and then up along the inside of the left front fender, preferably along side of the forward lamp harness. A trick here, (and no comments from the peanut gallery), is to use KY Jelly on the wire before fishing it through the grommet. Since the outer covering of the cord is rubberized, and the grommet is more than likely rubber also, the KY Jelly allows you to slip the wire through the grommet with easy, and since it is water soluble, it cleans right off with a damp rag. I just taped the cord to the existing forward lamp harness. Once you have the cord fished to the front of the fender, you will come out by the voltage regulator. Very carefully strip off the outer covering, exposing the BLACK and WHITE wires contained within. (You should have about ten feet of each hanging there.)

10 Terminating Volt Gauge Wire at Voltage Regulator

Step Ten is to connect the WHITE wire to the "power distribution splice" near the voltage regulator, via one of the two fusible links you bought. The "power distribution splice" is a group of three very heavy gauge red wires located in the forward lamp harness very near the voltage regulator, which are soldered together. You will have to open up the forward lamp harness to find it. I highly recommend you solder the fuse link to the WHITE wire and then solder it into the "power distribution splice" as well.

11 Routing Volt Gauge Wire to Battery Power Junction

Step Eleven is to take the BLACK wire and route it over to the power junction block by the battery tray. The best way to do this is to tape the wire into the forward lamp harness which runs along the top of the radiator support. The wire is held onto the radiator support via nylon clips which are taped into the wire harness. You can remove the harness from the radiator support by pinching the tabs of the clips with a pliers and push the tabs back through the hole. The clips will be reusable to reattach the harness to the radiator support.

12 Terminating Volt Gauge Wire at Battery Power Junction

Step twelve is to connect the BLACK wire to the power distribution block via the second orange fuse link you bought. Solder one end of the fuse link to the BLACK wire. Attach a round eyelet connector to the other end of the fuse link. Now attach the fuse link to the power junction block.

13 Reconnect Battery and Test

Step thirteen is to reinstall the battery, then test out the gauges. A: I used the above procedure on doing the swap. It was very helpful and I recommend anyone doing this to follow it. I did notice a couple of errors:

1. The pink wire that plugs into plug location #10 on the rally cluster connector is +12VDC, not Ground as stated in the procedure. The cluster gets it ground through the shield of the speedo cable. I added a ground wire to the speedo cluster by terminating one side to a screw on the speedo housing, and the other side to metal location on the steering column.

2. The unused "Generator" lamp (Brown wire on stock cluster) does not need to be cut. As stated in the procedure, there is a second Grey (connects to plug location #6 on rally cluster) wire required for the rally cluster's dash illumination, not supplied on the stock cluster wiring. The rally cluster's circuit card has a built in jumper between plug location #4 and #6, so an extra wired connection is not needed. Just tape off the unused Brown Generator wire in case you return the cluster to stock later. A: I would recommend buying a Lyle connector pin remover instead of using a screwdriver to remove the pins from the connector. You greatly reduce the risk of damaging the connector and the pins. It cost about $10.

I would also recommend not cutting off any unused connector pins. Just use heat shrink around the pin and tape the unused wire down to the harness. A: 68 ralley gauge pin location is: 8-illumination, 14-left signal, 15-right signal, 30-fuel sender, 31 -oil press, 33-brake warn. indicator, 35- water temp, 39-ign(batt), 105-ammeter(batt), 106 ammeter(gen) or alternator. tThese are the GM "circuit #s and are pretty much universal as far as the colors and the useage with corresponding #. I cant draw a diagram like above so here is pin 8 has a jumper that ties pin 1,3 - 30 is pin4- 35 is pin5 -31 is pin6-14 is pin 7-33 is pin8-15 is pin9-39 is pin 10-105 is pin 11-106 is pin 12. And I will restate this again for everyone that all 3 wiring harnessses must be changed to make this conversion work. NO SHORTCUTS. You CANNOT just change pin location. (68 Ralley gauge circuit board Diagram from the 68 Diagnostics service manual.)