For some reason the electrical box for my hitch keeps shorting out.  The first time it did it the moment I first hooked up the trailer to my hitch.  The second time it did it, it worked fine for 2 months.  Any ideas why this is happening.  I don't want to get stuck several hours from home with a shorted out hitch wiring.  U Haul put the hitch in and is using the box that my Saturn Vue called for, but the thing keeps shorting out.  Could the wiring on the trailer be bad, or have something to do with water getting into the lights on my trailer.  I'm not much of a electrical guy, but am getting frustrated replacing the hitch wiring every  month.  

If it blew the minute you hooked your trailer up to it I'd say you're wasting your time blaming the hitch harness.  You've got problems with your trailer wiring.  You could have a wire corroded touching ground, a wire cut touching ground or any variety of things. If your trailer is over 5 or more years old you might want to consider rewiring it.  It's not hard to do nor expensive.

If none of the lights on your trailer work at all I'd look at two things first.  

If your vehicle requires a converter box like mine I'd start there because it is the easiest to look at and is a source of problems for me occassionally (vehicles that have separate rear turn/break signals lights require them for trailer light hook up).  Where mine plugs in to the vehicle's wiring harness would often get corroded (under the back near the frame/body).  Unplug it and spray the connection with WD40.  Plug it in and un plug it a few times to help the WD work,  cover with dialectric grease (vasaline works too) and plug it back in.

The second thing is it could be an intermittent ground  which can be more difficult to pinpoint.  But I aways start where it is connected to the frame of the vehicle to see if it is corrodded/rusted.  A voltmeter makes diagnosing this a little easier so if you know someone that knows how to use one and has one they could be a big help.  With a voltmeter you can tell exactly wich wire is causing the problem and whether it is in the hitch wiring or the trailer wiring.

I agree with C7 if your trailer wiring is more than a few years old it may be time to replace it.  You may have to repalce the trailer lights too or at least the lenses.  If water gets into your lights when you dunk them into launch/load your boat it could short out not only the trailer lights but also the lights on your vehicle too.

Hope this helps.  I know wiring can drive you crazy (don't ask me how I know that).