48V to 12V Stepdown Converter Wiring for original "12v negative tap" system

[Shwagon]

Switching to lithium on a 48V Taylor-Dunn cart. Going off the wiring diagram, 12v accessories were originally run off a "12v negative tap".

Looking for clarification as a 12V negative tap system (and the existence of a circuit breaker on the apparent neg/ground circuit) is throwing me for a loop - Does this mean that the original "Hot" supply is 48V, but the circuit ran on 12v due to the battery grounding location on the series circuit?

If so, would I simply tap the original 48V hot and use the original negative tap wire as a 12V ground for a 48v/12v Step Down Converter?

*Use Zoom button in this link to see full size diagram: https://postimg.cc/zyT2s8CT