[Cbert]

I ran into an issue today while I was trying to wire my proximity sensors. I have a 3 wire sensor, one leg connected to my power supply+, one connected to power supply-, the 3rd leg is the output that goes to my bob. When reading with a volt meter I have 12v across the positive and negative wires, but I also have 12v across my positive and output wire. I am not sure how this is happening when the sensor is not activated. It is a normally open sensor.
To make sure it is not the sensor I have disconnected the sensor from my control box which is connected via an aviation plug. With nothing connected it has the same results. 12v across the positive and negative, and 12 v across the positive and output.
When I disconnect the output from my breakout board and have it attached to nothing it reads correctly. 12v across the positive and negative, and no voltage across the output line. None of the wires have continuity between them.

I am at a loss on why there is voltage going to the output leg only when connected to my bob?

I have a Ethernet smooth stepper with a c10 bob.

[Al_The_Man]

Are they sink or source proximity's?
A BOB with a source input requires a sink version Prox, and vice versa.

[Cbert]

Not sure how that would cause me to have the incorrect voltage only when connected to the bob, especially when the sensor isn’t even plugged in

[Al_The_Man]

You can still get a reading with a meter even if no pull-up/pull-down resistor fitted, you will get a voltage either way, is it PNP or NPN output?

[CNCMAN172]

Measure the output from the negative side of the power supply. As Al said these sensors come in PNP and NPN configurations, so you have the sensor model number. When you are testing the sensor make sure you activate it as well on/off. If this is a proximity sensor most need to be near metal, if it is optical you need to put something in the slot to block the sensor.