Hey All,

I'm in the process of creating a custom LED or TFT display for my shift to indicate which gear the car is in, as I lost my B&M gear indicator panel and wanted something a bit more flashy anyway.

I've figured out so far that I can pull the current gear from the PRNDL/ inhibitor switch using a 4bit decoder / NAND gate from the 4 signal wiresusing the below logic table:

Park Rev. Ntrl. O.D. Drive 2nd 1st
Signal A GND GND Open Open GND GND Open
Signal B Open GND GND GND GND Open Open
Signal C Open Open Open GND GND GND GND
Signal D GND Open GND Open GND Open GND
Grounded Signal wires AD AB BD BC ABCD AC CD


So in order to know the car is in drive, all four signal wires will be grounded, which will tell the LED to light up on the "3/Drive" indicator, or C & D for 1st etc etc

My question though, I'm assuming the triggers from these come from the actual inhibitor switch pins and are based on the gear selector shaft and it's physical position in relation to the switch, i.e. the clock position of the shaft will ground certain pins.

The signal wires from the transmission though I'm guessing are determined by the shift solenoids and whether they're engaged in whatever way.

Are the 2 mutually exclusive, and if so, how do I split them.

For example, if my car is in OD or drive, and I floor the pedal from standstill, will the signal pins be putting out the Drive signal the whole time, or will the transmission output the gears as the transmission goes through them? (1st,2nd,3rd lighting up and then overdrive)?


Once I have a working version with LEDs, then next step is to use a small screen and Arduino module to program it to display a Letter, icon or even animation for each to gussy it up a bit.

For reference, this is the dash I've built to accommodate all of this