Why Did a Fuse on My Boat Blow?

Question:

My marina just launched my boat and they informed me the port engine had a blown 90a main fuse. What would cause this? Age? or something shorted? Thanks, Rich 
 

Answer:

Hi Richard; thanks for reaching out to PYS. Difficult to say what could have caused a blown fuse,might be shorts, overloaded circuit, or sometimes even corrosion. As a first troubleshooting step, identifying what the circuit does ie. alternator output, charge circuit or starter circuit  and working out from there.