Brake indicator light will not go off

I have a 97 Mustang with 100,000 mi. The brakes are working well but the brake indicator light in the dash has started comming on shortly after start up. The intensity of the light is rather dim compared to the start up bulb test or when you put on the emergency brake.

I had new calipers and lines installed out of town about 8 weeks ago so I took it to a brake shop near home today. The tech bled the lines and said there was some air in the front lines ( probably from the out of town job not being bled properly) but otherwise the breaks were in good condition and that it was likely due to a sensor or faulty contact. He recommended going to the dealer as they may have a service sheet on the fault. I know tracing electrical faults can be time consuming so beforeI go to the dealer, do you have any idea what might be causing this?

Thanks,

Rick