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2014 Ford Explorer Sport
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The VSS output on photo 1 is sent to the PCM, E4OD transmission control, and Speed Control. It's output is the standard 8000 pulses per mile. You could tap into that VSS signal then send it to the PSOM input of your current instrument cluster. Set the calibration constant to 1, maybe zero?, so the PSOM will not try to divide the signal down. Or if you find the Speedometer/odometer is not accurate because of larger tires, gear change, etc. figure out a new calibration constant to correct it instead of changing the drive/driven gears.
 

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I suggested going straight to the PSOM since the 4WABS module is prone to blocking the VSS signal. In theory you could even bypass the PSOM as well, but having it in place makes it a bit easier to wire in and having the functionality of using it to correct the transfer case VSS pulses per mile. Just be aware the math to figure out the new calibration constant will be very different than the regular formula since the axle mounted VSS uses more pulses per mile because of the tone ring tooth count.
 

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I am not aware the 1991 and earlier PCMs and Speed Control used a different VSS signal standard than the 1992 and later. Both should be designed to use a 8000 pulses per mile signal. The PSOM divides down the rear axle mounted VSS signal so the computer (E4OD only), speedometer and Speed Control system will function.

If it turns out the VSS signal standard is different for 1991 and earlier I stand corrected.

I agree the 1992 and later transfer cases do not have the drive/driven gears to run the VSS signal generator in the OP's first photo.
 

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If the VSS output on the transfer case is 1000 pulses per mile as Kingfish thinks it may be, then the pulse count is too low to correct with the PSOM. The PSOM is designed to take the ~72000 pulses per mile VSS signal from the rear axle then divide it down to the 8000 pulses per mile the computer, speedometer and Speed Control system is expecting. The PSOM can only divide, not multiply.
 
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