Rears do NOT have wear sensors.
As itavaltalainen states, by unpluging the front sensor, you will trigger the warning light! Reconnect the plug - but check carefully for any damage to the wiring. Non-genuine pads are frequently prone to breakpad wear sensor failure (and OEM can fail too, if handled roughly). Also check for any corrosion within the electrical connector, and ideally seal and protect the connector with a smear of silicone grease inside the connector.