Preferred Pi, sensor for bilge pumps ?

[jabrockert]

I've got several Pi's running onboard, OpenCPN, AIS HAT, Pi-Hole, and now looking to add one for monitoring bilge pumps.

What is the preferred method to monitor these?
splice into the float wires and add
1 - Couple of resisters to knock the 12v down to 3v?
2 - opto-isolation like an 4N25?
3 - ???

JABrockert