Here is the circuit of a fuse is an automatic indicator status. This circuit can be added to a circuit that operates from 12V DC. As long as the fuse is intact, the LED D3 will light continuously and when the fuse blows the LED will flash and continue.
The first part of the circuit includes an astable multivibrator built around the transistors Q1 and Q2.The multivibrator output is coupled to the base of Q3 via diodes D2.When the fuse is intact, the base of Q3 retired to a positive voltage resistor R5. The transistor turns on and remains lit LED D3. When the fuse blown, the base of Q3 will no longer be pulled to a positive voltage bias and now only available at the base of Q3 will be the output of the astable multivibrator. However, the transistor Q3 will start the change in frequency of astable multivibrator and the LED blinks agree.
