converter

Absolute classic sign of the converter dying. Time to start looking for a replacement.

There are a few possibilities. As others have said, your DC voltage is fluctuating; the question is why.

Some multistage converters change their output voltage periodically per their programming. Progressive Dynamics with the charge wizard will (once the charge sequence has completed) jump from 13.2V to 14.4V for several minutes about once a day.

Some converters have wonky or varying output due to faults in the converter, and these should be replaced.

Sometimes there are self-resetting circuit breakers in various parts of the DC system, and a high load or a failing circuit breaker or a poor connection at the breaker will cause these to cycle on and off. Loose wires or connections can have a similar effect.

If you have a large varying electrical load, the voltage of the system will vary due to it. An inverter powering some nonuniform load is one example. Even a moderate varying load can often cause voltage fluctuations for the other things on the same circuit.

Sounds like the WFCO converter to me. Just disconnect the batteries and check voltage on the DC fuse board where the pos and neg land your answer is right there. If your lights are dimming or flickering, so is the voltage on your converter. Your batteries would not do that if your converter is working and you're plugged into shore power. Regardless contact Bestconverter and get something else.

Moved from 'General'

Fan only runs on converter when it gets HOT.

You NEED a multi-meter to check voltages.

Who checked the battery and how?

With shore power cord not connected to power, measure the voltage at the battery(s). Connect to shore power with cord and measure voltage again. When unpowered, your battery should be at 12.7-13 V. When connected to shore power, the voltage should be 13.5 V or higher.

Alternatively, you could remove battery and observe if the lights and other 12V devices work. If you still have 12V power, the converter is at least supplying some current.

Another way is to measure voltage directly at the converter's output terminals. When powered, the converter should supply > 13.5V.

For more focused advice, share the year, model number, and brand names. Some converters are known to have issues.