747 Classic.
One continuous fire detector loop is installed with detector elements in each of the main landing gear wheel wells. A fire or overheat condition in one of the wheel wells will initiate a fire warning.
The detector system is similar to the nacelle and APU fire detection systems except there is no discriminator. With an electrical short (detector failure) or a fire condition causing a short, the warning will be locked on. With a fire condition causing an open loop, the wheel well fire warning light will remain illuminated but will extinguish when the overheat condition has ceased.
With an open circuit in the detector loop the system will not respond to test. The brake temperature monitor module on the F/E’s panel provides a means of monitoring the wheels for an overheat condition.
I have some Boeing notes somewhere which say that hot brakes will not generate a fire warning.