by Michelle (Sudbury Ontario, Canada)
Question: I have a 2004 Coachmen Mirada motorhome with a 5500 watt Onan generator. My problem is the generator starts and runs well, however I have no power inside the RV, meaning the air conditioner and microwave, TVs and plugs.
I do have power to these units when I am plugged into an electrical outlet. I have 12 volt power for lights. A neighbor tested my generator and it was only producing 3/10’s of a volt. What could the problem be?
I accidentally started the generator while I was plugged into power. I fried the main circuit board. I did replace the circuit board and thought this would correct the situation but I am still having the same problem. What do you think it could be?
Any help would be greatly appreciated. I am trying to troubleshoot, since bringing the RV into repair shops is expensive, especially when you don’t know the exact problem. Many thanks.
Answer: Your problem is very difficult to diagnose remotely however we will do our best to help you. First let us say that unless your generator was an add-on and does not go through a transfer switch, there should be no reason why you cannot run the generator while plugged into shore power.
If you have an owner’s manual, try using it to diagnose the problem. Our Onan owner’s manual has a lot of good information and help in diagnosing problems. If you do not have an owners manual, try searching the Cummins/Onan website for your specific model.
Here is one link that may help: If that fails, perhaps this link will be of help for an Onan Marquis 5000 generator: RV Generator Handbook (Disclaimer: We are not associated with, nor do we endorse this site – we just found it in a search online)
There are several things that can cause the problem you describe: the generator circuit breaker(s) have tripped, a defective voltage regulator, a loose ground or hot wire at the generator, defective or broken wiring between the generator and the transfer switch or a defective transfer switch.
Another cause of low or no voltage can be worn brushes or broken wires to the brushes (by the way, some generators do not have brushes).
Good luck in diagnosing the problem.