Recently I completed a 3800SC and 4T65E swap into my 86SE Fiero. I ran into a small snag once I got the swap running and hopefully my solution will be worthwhile to people using either a Pisa or custom dash.

The problem was due to the fact that the Pisa dash is essentially only for a manual transmission. End result is I now had an auto and no indicator to show the gear I was in.

The schematic (for a 98 GTP – verify everything against your own schematic) shows that 4 wires come from the transmission park/neutral switch and go to the PCM and the instrument cluster to indicate the gear selected. I originally was going to figure out the binary for each position, decode it then output it to an indicator I would build with 7 LEDs in it.



I did make a schematic for that – a demultiplexer chip and a 5V power supply would work – but I decided there may be a section of the instrument cluster I could cut out that may make my job easier. I went to the junkyard and found a 97 Grand Prix and removed the instrument cluster. Following are two pictures of the cluster I ended up using.





Notice on the back of the cluster the small circuit board. This is the one you need. There is a ribbon cable that runs to it with 7 traces on the board. The wires are the 4 mentioned earlier, +12V, ground and a line for illumination. When +12V is applied to the illumination line, the LEDs will dim to the night mode. I removed the ribon cable connector and soldered wires in place of it to hook into the Fiero/4T65E system. Ignore the wire colors in the picture. I just used what I had.

[This message has been edited by AlanD (edited 10-07-2010).]

Here’s the breakdown of the board based on the orientation of the board with the pin numbers as shown in the second photo:



The following chart lists the wires that are grounded to light the respective LEDs on the board.



I ended up wiring the circuit board under the center console next to the computer. I got the illumination off the ashtray light and the ground from the screw on the passenger side under the center console near the computer. 12V can be pulled from any of the ‘HOT IN IGN’ wires in the C203 that feed either the fuel pump or PCM.

The LEDs I removed from the board and mounted on a remote circuit board that I milled an enclosure for. I picked up my LEDs from Radio Shack part number 276-330. The circuit board from the Grand Prix outputs around 2 volts to the LED so the ones I used worked well and were more than bright enough either during the day or at night when dimmed. I did not need resistors in series with the LED since they are on the Grand Prix circuit board. The LEDs are all linked on the ground side so only one wire is needed to hook that side of every LED up.

Not sure if I really described the whole procedure that well so if there are any questions please ask them and I’ll revise the writeup to reflect any info I need to add.

And here is the end result just awaiting the cruise to be wired so the console can be reassembled and mounted. Ignore the missing screw and zip tie. Still finalizing everything when that pic was taken.

[This message has been edited by AlanD (edited 10-07-2010).]

Do you know if this will work the the 4t65-hd also?

You would need to check the schematic and compare but I personally believe it will. If you have a specific car's transmission in mind I can pull the alldata schematic and let you know. I seriously doubt there would be any major difficulties as most of the range switches are similar

The schematic I show above is for a 98 GTP which I believe is for a HD tranny. I picked it out since it is a reasonable clear one and had the color codes that matched my setup.

[This message has been edited by AlanD (edited 10-07-2010).]