Bulb and battery method is fine-all you are looking to confirm is that the circuit is complete. Just disconnect at the plug and put a probe on each of the terminals of the yellow lead. Bulb should light. If it doesnt, yellow wire or sensor are at fault. The thin yellow covered wires that go to the sensors could fail - mine did on one of the rears. Didnt look frayed but had broken inside somewhere. If it does light, you are looking for a break in the wiring going the other way. More likely at the front near the struts as the wiring moves with the angle of the wheels. HTH