Multiplexing?

Brcidd is right.  These wires transfer data similar to the transponder receiver wires.  They're usually not meant to carry a data signal very far, but the fact that it's a serial communication (as opposed to a parallel communication) does provide for the data signal to transfer from a... say... truch ECU to the primary Body ECU on the firewall (under dash) without a problem.

These wires can't be tested with a DMM or any other type of tool because they do not carry voltage.

This is where factory OEM wiring diagrams come in very handy.  Expect to see more and more of this as automobile wiring technology advances.  I just hope that DEI and other manufacturer's can keep up with innovative products that will EASILY interface with these new data systems.

Here's to hopin'