The Magnetek converter-charger TU-740-2 probably includes the circuit breakers and fuse panel in your RV. Some models also included an inverter.
These devices all have a 120 volt input. That input most likely comes from the circuit breaker panel. If you have an inverter, it will also have a 120 volt output. (An inverter converts 12 volts DC to 120 volts AC.) Do you have an inverter?
They all have a 12 volt DC output. It probably has two 12 volt outputs. One goes to the fuse panel. That would be the converter output. (A converter changes 120 volts AC to 12 volts DC for house lights, pumps, and things.)
If a second 12 volt output is present, it would go to the battery for charging.
Replacing with a modern converter charger.
Modern converter chargers usually have only one 12 volt DC output. The charger and converter function are combined into one. The two 12 volt outputs can be combined into one.
The converter/charger portion of the Magnetek can be replaced independently of the circuit breaker panel. See the following:
Here is a schematic that may match yours.
This company may have an upgrade kit for your converter charger. The company provides expert advice on how to do the upgrade.
Check under "Contact Us" menu selection.
I wish you good luck and happy trails ahead!