The first thing I'd check is to see if the lights are operating properly. I'd specifically check the voltage at the lights.
One issue many people do not realize is that in high current DC applications, the wire size typically needs to be much larger than what it seems. The culprit here is voltage drop - especially with distance, not lack of current.
In other words, the wires could be fully capable of carrying the required current, but not be sufficiently large enough to supply the required voltage.
The conventional rule of thumb is that for critical components, there should be no more than a 3% voltage loss from the battery/alternator to the lights.
Three percent means for a 12VDC system is only a few tenths of a volt.
Therefore, the first check I would make is to measure the voltage at the battery with the engine running, and again at the lights and compare the two.
If there is more than 1/2 volt loss, then I would suspect the wires, light switch relay, etc.
If it is OK, then it might be that the bulbs are just not that powerful, and you might be able to upgrade them. However, if the replacement bulbs require more current than the old ones, you may again be up against loss of voltage due to wires, or exceed the capacity of the light relay, switch, and so on.
I am not saying the wiring is the issue, but the starting point to me would be to measure the voltage at the lights and see where it takes you. This should be a simple test, and especially if you can easily access both the battery and headlights. Something as simple as a relay, switch, etc. could be going bad - not allowing full brightness.
Of course, other factors, such as yellowing plastic headlight lenses can affect brightness too, but I would be surprised to see that on a 2011 vintage coach.
These are just a few of my random thoughts.
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