fan in circuit-breaker box is cycling every 10 seconds

Question...Are you parked, plugged into shore power and disconnected from the tow rig when you noticed this? If so.. Have you moved the TT since? IF you are parked with shore power make sure you didn't accidently engage the electric brakes. If you moved you obviously could feel the brakes drag but check the pin on the emergency switch. This happened to me. The pin got pulled out slightly, didn't notice until the extra load caused the fan to run to cool the converter. Seems unlikely but something to look for.