One wire has continuity to ground at all times. 12 V DC during unlock and ground at rest. Another wire has continuity to ground at all times. One or two of the wires has continuity to ground at all times. One wire always shows continuity to ground.
Polarity changes on one lead during lock and on the other lead during unlock.
If you are dealing with an aftermarket door lock system, locate and measure each coil lead of the lock and unlock relays. Then connect to the leads that activate each relay accordingly. These will usually be negative inputs. Some will have both positive and negative inputs to work with any alarm or keyless entry without the need for additional relays. Special These applications will be similar to others, but will require additional connections, parts, or both.