Brake Pad Warning Light

My brake pad warning light (1980) formerly came on and went off, often on the same trip. My pads are 80%. Now the light comes on and stays on, along with the irritating ! which I can't extinguish. All sensors have been examined and connectors cleaned with no change. Is there something else to check, or is the next step to replace all 4 sensors. I could also just live with it I suppose.

The brake pad warning is created by an open in the circuit diagnostic wiring.  The brake pad wear sensors are just a sacrificial component that when it wears away it creates an open circuit to trigger the warning.

So, to test the system you open each brake pad wear sensor connection.  To test the brake pad wear sensor itself, just check that the circuit at the connector.  If it is a closed circuit (zero resistance or no open circuit with a continuity tester) then the sensor is OK.  If it is an open circuit, the sensor is broken or worn.  Bridge the sensor to chassis connector plug.  If the warning light goes out, the problem is with the sensor or sensor connection.  Repeat for the other wheels.  If the warning stays illuminated and all wear sensors check OK, the problem is an open circuit in the chassis wiring or failed diagnostic module.  

Sadly, many 928s have old crumpled wiring at the wheels which results in an open in the circuit somewhere.  Replacing the wiring harness is difficult.  My 1987 928 with over 195,000 miles now has the pad warning lamp on and the senors and pads are good.  I'm living with this issue, on my car I can cancel out the central warning lamp but the small warning message remains illuminated in the instrument cluster.

Thank you Rich. Everything I need to know.