Dear Tonigalea,

If I undertood very well your problem the solution can be as follows;
First of all you should use 2 pcs. 4067 (analog multiplexer)
'------------------------------------------------------------------------------
mux1 var byte
mux2 var byte
shft var byte
error var byte
InputA var PortE.0 'connected to the exit of Mux1
ExitB var PortE.1 'connected to the exit of Mux2
Input InputAutput ExitB

main: High InputA
for mux1=0 to 15:error=0
for mux2=0 to 15
shft=mux1<<4
PortC=mux2+Shft
if ExitB=1 then Error=Error+1
next mux1
next mux2
if error<15 then Broken_Line
if error>15 then Cross_Connection
'------------------------------------------------------------------------
'The ExitB should be Pulldown by a 10K resistor.
I did not try the program but I think it can work. You can check broken lines and also cross connected lines in same time.

ERO