Ground Fault in Underground Wiring?
Even if the conduit is flooded, the wires should be completely insulated from any water.

I would use a voltmeter to see what is happening electrically with the wires.  If the neutral or ground wires are not at zero volts, then try to determine where the bridge from a "hot" wire is.  Hopefully it is in a junction box in the garage or house.  You can probably narrow down the problem by temporarily disconnecting the bridged wire at one end and then the other and seeing which direction the feed is coming from.

Only if both ends are disconnected would that indicate a failure inside the conduit.  Then you could try evacuating the conduit with a shop vac and see if that has an effect on the problem.  If so, it is time to replace the wire inside the conduit.  You need not dig it up.  You ought to be able to feed a replacement wire by attaching it to the old as you pull it out.  Be sure to use generous amounts of silicon lubricant so it gets easier as you go&mdash;and to make replacement easy next time.