I too have a Burro
and have done extensive updating.
The typical electrical
configuration, and I say "typical" because the interior of the Burro was often a kit that the original owner installed and this provided options.
There were no converters in the Burros. The shore power (120VAC) only powered a single fluorescent light
and a power outlet and the optional 3 way Dometic 211 fridge
. The light fixtures on either end of the kitchen cabinet are 12VDC as is the Cat heater. There never was a factory option for a water pump, only a hand pump/fawcett. There was no original fan. Some owners when putting together their interior kit put a battery
into the unvented compartment under the bunk (dangerous), and others made room for it on the tongue.
This is the extent of the factory supplied electrical system.
If you have a buzzing sound when connecting to AC power then someone may have installed a converter or a simple charger. Look for this in the forward driver side compartment. This is the typical place to install such.
The good thing is that all the wiring in the Burro is exposed and easy to get at and do updates.
The CAT heater has a gas line running from a T under the stove and uses 12V power coming around the back with black and white wires. I removed my heater out of fear of using it in such a small space, and the need for more storage. We now have a door over that space which is now a cabinet. If you are determined to get the heater to work, go to the mfg web site as they still have lots of info about the heater. It might even still be a current product, or at least it has not changed much.
The document center here might have the owner's manual for this heater. If not and you need it, get back to me as I have the original manual which came with my Burro.