My rally gauge ammeter quit working. Is there a schematic that shows how the ammeter circuit is wired? I've looked through the Pontiac service manual and Firebird supplement, but didn't find anything specific to the ammeter.
The diagram is elusive, never did find one. Is yours stock?
I added my rally set, and connected the ammeter to the large guage red accessory wire on the horn relay and the green lead on the regulator. Only place I could get the proper potential difference to run it.
Thanks, Dave. Yes, mine is stock. I'll probably start tracing the wires and probing the connectors with a meter. A schematic would give me a feeling that I knew what I was doing.
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.)
That explanation is WRONG, I tried it to knowing it was faulty. You cannot get potential difference on two ends of the same wire!
I beat my head against the wall then Jim (fbody) had a suggestion to try the second wire on the brown reg wire. it pinned the guage, so I tried the green one. BINGO. Works perfectly.
If your guage is good, do a continuity test on either ends of your Black and White wires to pinpoint the faulty one...
Last edited by Dave's White Rock '68 Droptop; 11/19/0902:55 PM.
I think I follow what your saying "You cannot get potential difference on two ends of the same wire!" I thought the same thing when I read through that too.
Where is the green wire your talking about that you tied to?
I sent a email out to M&H for myself to try and figure out where the factory connection points are under the hood.
The green wire is on the plug connecting to the voltage regulator. I pulled the tab out and soldered the wire on and plugged it back in. As I said the other wire goes to the horn relay where the heavy red connects. That also saved running the wire accross the radiator core mount to the junction box.
Can't recall which one goes where, but if it shows discharge instead of charge just reverse them.
Under normal conditions I get only about a needle width advance to the positive side, altho after starting it sometimes goes about 3-4 needle widths to the pos side for a few minutes.
I talked to M&H tech support today bassicly asking where the two tie points are on the forward lamp harness.
One goes to the Battery junction point that gets jumpered again at the horn relay.
The other is is suppose to tie at the Alternator.
Seems like the same point to me but he explained how it worked not that it made any sense to me but their should be a small difference of potential to work the gauge.
For me this means I should be able to measure from ground to either the black or white of the Cluster Gauge plug and read 12 Volts. I can also do some continuity checks with the battery disconected. I'm not going to look at it until spring and may end up calling back for more details if needed. If I can I will document the whole thing and possibley make a drawing. My set up is a little different in that I have the internal regulated alternator.
Yes, I have the external regulator, but you are correct in your case, as the reg is internal, you will tie in the other wire there....just not sure which point.
I finally had a chance to look at my car today. The ammeter wiring is exactly as described for the Rally Gauge wiring in the Q&A FAQ. Thanks for pointing that out, rohrt. I forget to check that area, and it is full of great information.
Anyway, the black/white wire connects to the power distribution splice, and the black wire connects to the junction block. I removed the gauge cluster and verified that there is 12 volts at both pins 11 and 12 of the cluster dash harness. I put an ohmmeter across the ammeter terminals, and it read 0 ohms. It is possible that the gauge is shorted out. I will have to look into it some more. I put my volt meter across pins 11 and 12 of the cluster harness and measured 40 mV with the headlights on, so there is a measurable voltage drop. It does make sense - there will be a voltage drop whenever current flows through a wire. The drop will be dependent on the current flow (amps) and the wire size and wire length (ohms).
I want to do some more testing of the ammeter gauge to determine what voltage drop causes a full scale reading, and put known currents through the power wire going across the radiator core support and measure the resulting voltage drop.
I never measured the ohms across the amp meter but I would suspect the it would be very low. When I check the amp meter with the 9v battery and the pot I peged the meter hard. I had to realy turn up the resistance on the POT to get a good reading with the needle. I would suspect the gauge is very sensitive.
The green wire is on the plug connecting to the voltage regulator. I pulled the tab out and soldered the wire on and plugged it back in. As I said the other wire goes to the horn relay where the heavy red connects. That also saved running the wire across the radiator core mount to the junction box.
Just to get some clarification on this, I don't have a green wire on my voltage regulator. I do have a slightly faded blue one. Before I destroy my ammeter, i want to make sure this is correct. I attached a few pics and diagrams for help. Is this where you all have hooked up the ammeter?
No wire is a perfect conductor. There will always be a potential difference when current flows. The amp meters are very sensitive to this. This was a much better design than running all the current through the cabin like Chrysler did.
Thank you David! If you wouldn't mind verifying, I think I may just hold off until then. That car has gone 44 years without displaying that info. It can wait a little longer!
Where you ever able to get your Amnmeter to work wiring it like this? I'm in the same process of installing Ralley gauges, but following the write up on the FAQ front page (routing black wire to the battery junction block) it does not work.
