The advice you have gotten is about all the maintenance you can do. Sam's advice should be followed. Those connections can sure get loose. That was Glen's problem (Muldoonman). We will get to his issue in a second.
What I would do is pop the cover off the transfer switch and see if it has one relay or two. Some of the less expensive transfer switches have only one relay. They usually default to the generator as was stated above.
If you have a voltmeter and are not afraid to use it, check the leads coming into the transfer switch from the generator and see if you have voltage. If you do, the coil in the contactor/relay is not working properly, or is burned up. If you do not have any power from genset, check the breaker on the genset. If that does not get you going, let us know so we can help you troubleshoot the generator.
For those who are interested in Glen's problem, here it goes:
He brought me the coach and said the generator would not produce power.
I checked power at transfer switch and had about 60 volts from L-1 to N or L-2 to N, but nothing across L-1/L-2. I went ahead and flashed the field knowing it most likely was a bad regulator. Flashing did nothing.
I started to prepare the generator to come out. While doing so, I remembered not long ago, he had a no power issue and the main breaker was tripped on the generator. I decided I had better pull the cover off of the breaker enclosure on the genset before I went any farther. When I opened it up, I found burned wires, melted plastic and just a general mess.
The problem turned out to be one of the neutral wires had burned through the terminal block inside the breaker box. The breaker was hanging by the wires in the bottom and the top was held on by magic.
Upon really looking at the connections in the box, everything was loose. I showed glen, we bought a new enclosure/breaker and problem was solved.
He also has a small load imbalance between L-1 and L-2. This can cause generator failure as well as make the neutral carry too much current. I will juggle some loads around tomorrow and see if I can't get things a little closer. All the loads in his coach are 120 volt, and with the amenities that coach has, it needs all 50 amps. If he did not want to keep the option of powering his home from the coach, I would recommend he let me reconfigure the genset to 120 volt only.
Sorry for the novel above. Maybe someday I should start a blog or something......