Lots of great suggestions here -- thanks! I never would have thought of washing it out with water, but of course the connections get wet in the rain. So water should be ok.
And obviously, I will try dry methods (vacuum and air compressor) first. Then water. The let it dry and blow it out some more.
The screwdriver idea makes sense -- I can insert the blade gently to open up a gap so the grit can be blown out.
I am reluctant to try WD 40 -- I'm worried that it will trap more grit.
Someone suggested taking the unit apart -- it's a one piece molded item and can't be disassembled.
I've done a lot of off road towing, and I have never seen so much dust and grit in my equipment as we experienced in the Mojave Desert. Wow!! Might be a good idea to wrap some plastic around the 7 pin next time we go there, as suggested above.
