We have a V8 2007 Dodge Durango and recently we had a lot of water/flooding in the area. We drove through some water that was about 2"-3" deep and we drove slow through it but after that one of the two horns doesnt work. Both when pressing the horn in the center of the steering wheel and when locking with key pad.

Did the water short out something or maybe a fuse went bad at the same time some how?

 

Two to three inches deep, or two to three feet deep? 2" to 3" is nothing, 2' to 3' is another matter.

Have you tried using a voltmeter or multimeter to see if power is getting to the horn that isn't working?

 

it was only inches of water so the only thing I could think of was the water splashing up got into the horn it self and shorted it out. How do I go checking the voltage?

 

You're not really checking the voltage necessarily, you are checking to see if ANY voltage (any power) is getting to them. This will tell you whether the horn itself is bad, or whether the problem is somewhere before the horns.

Its simple. Locate the horns (Haynes manual would probably be good for this), should be two wires going to each one. A voltmeter has two prongs... you can figure out the rest.