Onan 17 KW electrical problem

I have a 2002 Novatec 55 purchased last season with a 17KW, MDKAD generator. The unit has 1800 hours and runs good. Recently when running the unit I only get 110v, no 220v from the generator. This began early July 2025. Meter check shows 239v leaving the circuit breaker on the unit but showing minimal voltage at the main breakers in the panel. There are two selector switches, Panel 1 and Panel 2. The switches have five positions being; Shore cable, Generator, Off, Cable 1 master and Cable 2 master. All three cable positions have no less than 220v. I had two technicians check the system. With the selector switches on the generator position, the first said the selector switches need replacing. The second said only 119v is showing at the main breakers. I followed the wiring from the unit to the panel as best as I can and cannot find any other inline breaker or fuse. I find it difficult that both selector switches would fail at the same time. Has anyone had a similar issue or has heard of one. Also looking for recommendations for a marine service in the Upper Chesapeake Bay area that I can contact. Thanks in advance.

Sorry if my post was a little vague.
The gen-set had always delivered 220Vac until recently. The ships panel has two sides powered by two selector switches. One switch for panel 1, and one switch for panel 2. Each panel side has two Amp meters and one Vac meter. There are no 110Vac meters.

Both Techs used a hand held multi-meter to check the supply from the gen-set and the meter showed the gen-set was producing 239Vac. The second Tech checked the system using all four sources of incoming shore power and gen-set. The three shore power cords energized the panel with 220 Vac and all electrical components worked. The gen-set power switch did not display any 220Vac and would only produce 119Vac and 117Vac respectively at the main breakers. The second Tech then conducted a by-pass of the gen-set switch and received the same readings.

There is a smaller "box" on top of the gen-set which houses a manual stop/start switch, push button breaker, hour meter and electronic components and the supply Vac breaker. Additionally the second Tech observed the gen-set having an isolated common and ground wire. He claims that normally they are tied together at the gen-set but it is unknown why they are isolated. As the gen-set had worked previously the wires were left isolated.

Here are photos of the electrical panel and switches. The switch handle blocks the shore power chore setting at the 9 o'clock position.

My questions are has anyone had a similar situation and solution, and are there any recommendations for a marine Onan generator facility in the upper Chesapeake Bay that I might contact.

A reading between the hot legs was taken showing 119V and 117V respectively with the selector on gen-set. No or minimal Vac was shown on the 220V side. On all shore power cords the 110V readings were similar and the the 220V side showed 239V and 237V. I'm beginning to think the selector switches are the issue but I find it difficult to think both switches would fail at the same time.

The 239V reading was after the gen-set going to the panel.

I'm not familiar with running a "temp-test" wire but the distance would be approximately 25 feet.

I've loosened and re-tighten the common and ground terminals with no change. I did check all terminals and none were found loose. All the wiring appears to be #6 gauge wire.

There were very little ship documents and I do not have any schematic or diagram for this vessel. I believe I'm the third or fourth owner. Nova Marine in Taiwan did supply a very limited wiring diagram for a similar vessel but not for the one I have. I am in the process of searching for replacement selector switches as some of the terminals show some corrosion. Nova Marine did not have any information on the selector switches and stated they were imported from NewMar Marine in the US. NewMar Marine (CA) is a wholesale only company and I am reaching out to one of their distributors for assistance in trying to locate replacement selector switches.

In the meantime I will be searching to find an Onan tech to look over the system.

Thanks for your insight and suggestions.

I'm not certain what make the switches are. The numbers on the switches are; C42 / U93112 / SGB198.
Hope these photos help Identify the switches. The C42 plate has a make/name above the number and it looks like it ends with the letters "MIMER".
I will be going back to the boat this weekend and I will try to get a better angle to read the full name above the C42.
Thanks.

One thought in the back of my mind was to disconnect the terminals on the switch and clean them up, then reattach. Is that what you may be suggesting?
Yes, there is an AmTrack station not too far away. Why are you asking?