I recently needed a foot switch to control a DC load.  

This was actually for a hot wire foam cutter I winged, and it worked great... as long as I did not let the wire heat for too long without actually cutting material.

To mitigate the latter restriction, I added a foot switch.  By shorting across the plug on a stock intermittent AC foot switch, you then you get your switched output from the mains terminals on the cord end.

Yes, a binder clip was sufficient for the current I needed.  :)