I drove in flood waters now my car won't run

water goes into places you don't want, take air and disconnect all your connectors, all the electrical components must be free of water. Blow each connector both sides, if you have penetrating oil spray it in the connector, it displaces water aswell.

don't drive in "flood waters" it ruins cars- if submerged, it ruins all the electronics- if this is what happened, the car is a write off- it's not cost- effective to replace the whole electrical system- and a warning to the next person who might buy that car- it may be cleaned up, but it is ruined-