Doc here,
imp:
The ECM Controls the Vss, It is Pins 33 , Pink/Orange , and 58 , Gray / Black.
The diagram does not show an output to the dash head unit ..but I'm sure if you follow the bundle back, that's where it will be. Is it an LCD Dash?
You can get a pulse generator for the GM transmission easy enough, but to interface it to the Explorer wiring may be tricky..Do a Goggle search on Electronic Speedometers..there are several places that make the Pulse generators,and may have a pre~Made harness for interface.
The ECM also controls the Tach function, Pin 48 , Tan / Yellow wire ..If it's internal calibration board is set for 6 cylinder , there is not a whole lot you can do..Except replace it with a 8 Cylinder tach.
There is one remedy if you feel up to the task..AND It's a Mechanical Tach..
Get an 8 cylinder aftermarket Tach, Remove the calibration board carefully from inside it, At the back of the meter you will find two wires, + and -, these will go to your stock head unit meter when you switch over. mark them as such.
Go to the local electronics store and get a project box (plastic) that will hold the calibration board. Mount that in the box, drill a hole big enough to get the wires out of in each end..
Remove your stock Calibration board, and extend the wires from your project box to fit inside the stock meter housing, hook up the + and - wires to the stock meter.
Next hook up the red wire from your project box ( aftermarket tach wiring) to switched power , The Black to a good hard ground. Lastly hook up the gray to the - side of the coil..
Tie up the project box with tie wraps to a handy wire bundle, and you have an 8 cylinder Tach, with a stock meter face (no one will know but you.)
Doc
imp: