The connectors I used are as follows:

For the C2 connector (34-pin):
You need two of these as you have to destroy one half to make the other half fit (16 connections). So, then you need to destroy the other half on the second connector to make the bottom half of the new connector (the remaining 16 connections for a total of 32). The cluster C2 connector is actually 34 pins but pins 17 & 18 are not used so looking at the connector on the cluster the left most pins do not need to be connected so just plug your homemade connector in to the remaining 32 pins (right justify when you plug it in).

Metra Reverse Wiring Harness 71-2001 for Select 1994-2004 GM Vehicles

For the C1 and C3 connectors (11-pins each):

You will have to trim these down to fit inside the C1/C3 connector and line up the alignment notch (the part of the connector that has an opening or notch in it) to the pins not used on both the C1 and C3 connectors You should be able to see that I matched the notches up to align together.

Metra Reverse Wiring Harness 71-1858-1 for Select 1988-2005 GM Vehicles 32-PIN OEM Radio

In the description this is listed as a 32-pin connector for a 32-pin OEM Radio which is NOT correct. The connector is obviously a 20-pin connector and the two half's come apart easily leaving you with two 10-pin connectors, one black, one gray. So, the connector is correct, the description is not.

Modifying the connectors is up to your ingenuity. I used a Harbor Freight 2" chop saw to modify mine. Don't cut your fingers off!

WARRIOR 0.9 Amp, 2 in. Mini Cut-Off Saw

https://www.harborfreight.com/09-amp-2-in-mini-cut-off-saw-70478.html

I searched for several hours trying to find the original OEM connector so I could make my own, but I can't seem to find these OEM Delphi-Packard connector anymore. The problem with the connector (the 34-pin one) is that the pins are on the outer edge of the housing, where the connectors I can find (and say used on the 84-89 Corvette clusters) have the pins in the center of the housing. Maybe someone knows where to get these original OEM style connectors for this cluster and if so please let us know so it would be much easier to build up a matching connector.

Hope this helps!

Regards,

Xenawise

 

I have ordered the PCB's so I should have them by next week. Now to order the parts so I have them on-hand when the PCBs come in and build probably two of them right away. I will take some pictures of the finished build and of the tester in action. Looking at building the interconnects to the cluster from the tester right now. Need an easy way to connect to not only the GTA Digital Cluster, but to say the analog cluster as well. And to any other cluster that (mainly GM) still uses the connections provided by the tester (pre-Data bus clusters).

Stay tuned!

Regards,

Xenawise

 

Thanks very much for those resources.

Now, if anyone repaired the LCDs!

 

Got in the PCB's for the VSS and Tachometer simulator. This is not the full digital cluster tester PCB which actually just finished manufacturing and will be shipping to me soon. This is a small PCB with only the VSS (Speedometer) and Tachometer simulator circuitry on it and should be able to be used with non-data bus (pre-ODB-II) OBD-I GM clusters to simulate the Vehicle Speed Sensor as well as the Ignition coil for the speed signal and RPM signal for the speedometer and tachometer.

I got in five PCB's and built up two of them today. Here are a few pictures of the PCB:





Here is a screenshot of the 3D version of the PCB:




You can adjust the RPM with the control on the left (Tach), and the speed with the control on the right (VSS). It runs from 5VDC (not 12VDC, I fixed this with the Digital Cluster Tester as I included a +5VDC regulator on that PCB) so a USB power bank could be a great power source. You would just have to hack up a USB cable and hook up the power leads to this PCB.

Here are some video links to so you can see the odometer mileage incrementing (to test the odometer is actually reading the VSS signal and increments the mileage) and the second link is showing the speedometer changing and then the tachometer changing on the Trans/Am GTA digital dash.

https://drive.google.com/file/d/1XwR...ew?usp=sharing

https://drive.google.com/file/d/1hE0...ew?usp=sharing

Not sure if anyone would use something like this, and if there were interest, I would update the PCB with a +5V regulator so this could run from +12VDC as you will need to power the cluster from +12V so you could run this from the cluster power also.

Upcoming PCB just shipped to me is the Cluster Bench Tester. It includes this VSS and Tach signal generator along with switches so you can check everything on the Digital Cluster. Also, it includes all the switches so you can also check the DIC (Driver Information Center) found in these cars along with the Grand Am of the era. Here is a screenshot of the production PCB being shipped to me:


I just got all the parts for this yesterday, so when I get the PCBs in the mail, I can build up two of these for testing and see how they work. I know J.C. Denton expressed interest in this one. I designed this one to be used with multiple different clusters. You will see how I do this with a standard DB-37 connector that will have all the signals that this bench tester can perform. Then you need to wire up a mating connector that goes to the cluster of your choice. Some clusters have other features that the Trans Am Digital cluster does not, so you might be able to use one of the switches on the tester for these extra functions such as the Odo Memory switch if you need switched +12V or the Hidden Gen Lamp switch if you need switched ground signal. There is some flexibility here for different clusters, but the design of course was for our Trans Am Digital cluster.

Let me know what you think and any comments!

Regards,

Xenawise

 

Very great, I am absolutely interested in the "complete digital dash tester" that includes all test functions. We just need to find someone who can identifiy the factory connectors for the digital dash, maybe @vorteciroc can help here. I would love to have a bench tester which I can plug in a digidash with DIC and test everything of it. The digidash os not found often here in germany, but a few guys who have it, have problems with this and nobody over here is able to help or even test this 80's thing.

 

This Thread is AMAZING!


Please PM me regarding anything that I can try and help with.

 

Folks, I can confirm that the Digital Dash & DIC Tester does work! I have not managed to get a connector for my DIC just yet, so that portion remains untested, but the rest of the tester does seem to work as it should. Here are some pics of it working:

Tester PCB fully built and connected to the GTA Digital Dash:


C2 Connector plugged into Tester PCB:


C2 cable from tester PCB to DB37 Female Connector, plugged into a DB37 Male Plug which is wired up to the handmade C2 connector plugged into the C2 connector on the cluster:


C1/C3 cable from tester PCB to DB25 Female Connector, plugged into a DB25 Male Plug which is wired up to the handmade C1/C3 connector plugged into the C1/C3 connector on the cluster:



Digital Cluster Tester sitting on top of GTA Cluster and set for 140MPH Speed, 4500RPM Tach, 3/4 Fuel tank level, 35PSI Oil Pressure, 200 Degrees F coolant temperature, 14VDC voltage, and all the bulbs lit (left/right turn, high beam, BRAKE, Service Engine Soon and Fasten Belts). This cluster is from a 1988 GTA so the SECURITY bulb was not installed from the factory since the VATS system was introduced later in the model year (I believe) or in 1989 which the digital dash was discontinued.


Continued next post...

 

Close up picture of the Tach, Speedometer, Fuel Gage and Oil Pressure, Coolant Temp and Voltage Gages --- Also notice the Up Shift indicator in the Tach LCD Display is turned on as well:


Picture of the Odometer LCD showing the Average Speed of 139.5MPH! Yes, the Odometer does count up the mileage and with the Odometer Memory Switch enabled, the odometer will remember the km/h or MPH setting even if you switch off power to the cluster as it was designed to do.


So, seems to work OK so far. I need to adjust some resistance values for the coolant values since they are not matching the PCB silkscreen, but I want to match the actual LCD display instead so something around 190- or 200-degrees F should be the center switch position. Right now, the resistance value for 100 degrees and 220 degrees needs to be adjusted to better display on the digital cluster. Of course, the Variable control will sweep through the entire range so that will work if you want to set a specific value.

I need to find a connector for my DIC display so I can get that wired up to the tester and get that portion checked out.

Perhaps I need to PM vorteciroc and see if we can source the factory connectors for the cluster as well as the DIC so no one has to hand build these connectors.

Just wanted to post up these tests and to let folks know I am still pursuing this project to completion. I realize it is a very, very niche project, but I also have designed it in mind to be used with other GM clusters of this era as well so that could broaden its use case.

Please let me know your questions or comments!

Regards,

Xenawise

 

Incredible work Xenawise! There's not many people left anymore willing to take on a project of this depth, much less with actually designing new testing hardware. Having replaced individual board components in my own dash over the year, I can appreciate what you've done here. You'll have interest for years if you shop this around in the enthusiast groups.

Cebha helped me out awhile back with a replacement odometer chip and honestly, the time he put into reverse engineering the programming logic for something that seems so simple is on another level. It's an overlooked feature of the car i appreciate and after 40 years, really every part of a car is a maintenance item that needs replacement XD.

if you're still programming out new ones, I'll flip you a message to pick one up. At some point, mine partially corrupted and usually no longer displays a clear number if there is a 2 included. I rolled over 200k awhile back so that's a bit of an issue now.

 

This is truly awesome. I might be interested in a test setup myself.

Do you do any new design? I watched a video of a guy who programs and was building simple displays. I thought about how an Arduino could be used to drive a cluster with new LCDs. I would love to make a new screen setup, but programming is difficult for me

 

I just signed up at thridgen because of this thread! Just bought a 1988 GTA and the odo screen is missing so I am suddenly interested in finding an odo screen if anyone can spare one please DM me.

Being in awe of the great reverse engineering that has been done here I also would be happy to somehow help to preserve digital dash functionality. Xena, are you open to selling another one of these complete test boards? and do you have several of the 2801 programmers to sell one as well? I can't find those anywhere; dasaro seems to not sell them anymore.
Steve