check it first with a dmm to make sure your sender is outputing a voltage
I have a FB4 connected to an oil pressure sender.
The sender was three wires; 12V power, GRND and signal 0-5V
I have connected power and ground to a power and ground not on the board.
That leaves one wire only going to the brain's analog input signal.
I'm not reading any values on the input.
Do I need to connect the FB input ground to GRND?
Can I connect the sensor GRND to the FB input?
I have and it is. Reading was about 4.7V
The FB and the sensor share the same ground (the car) but the input ground is not connected to anything.
The easiest connection would be to connect the sensor ground to the FB input ground but as it is powered from 12V I'm reluctant to try that in case it fries something.
check out this link:
looks like you may just need a zener diode