Left rear of cylinder head (single wire sensor)
On the fuel filter!
It is on the pass side front of the engine.
by putting water in the gas tank
$ 40 from Rockauto.com
A 1998 Ram with the Cummins diesel has a water in fuel indicator on the dash that will illuminate if there is water in the fuel filter housing.
It is the smooth pulley next to the belt tensioner.
approx $250.00 if you do it yourself
That is the fuel filter on the driver side of the engine block.
It is the two wire sensor near the thermostat housing.
The water pump is to the passenger side of the fan drive, and the thermostat is under the upper hose attachment.
Water drain and water in fuel sensor.
most are near the water outlet housing.