The letter will be "R". The code 1R means that the genset is set up for remote start.
If the genset is running, it should be producing power. If it is not producing power, it would shut off as soon as you released the start switch.
You can easily check, though, by simply opening up the control box, and testing for voltage directly at the back of the circuit breaker with the unit running.
Follow the genset leads. They will lead to a junction box that is usually right next to the genset. Make sure that the connections inside the junction box have not come loose.
If they are good, follow your shore cord. It will lead right to the transfer switch.
If you have good genset power going in to the transfer switch, but nothing coming out, the transfer switch is bad.
Also, another thought. Some of these older coaches did not have a transfer switch or a receptacle. Some had a manual switch inside the coach. Check to see if you have one of those, and if it is in the correct position.