Well to use a semiconductor solution (transistor, opto, etc) you really need to know something about those two wires you 'cross'. What is the open circuit voltage, what is the polarity or is it an AC voltage, how much current flows when you 'cross the wires'? If you don't know those values then you are better off using a standard relay as the contacts will work without having to know those things, except possibly how much current is being switched on and off.
Lefty