Old school 6 fuse wiring is not modern PCi 100% computer data BUS controlled. W124 was both petrol CRD if my memory serves me.Always on by the milli-second software driven constant checks on lights, alarm points, etc are the reason. Ditto the original OEM radio is coded to the BCM module (caveat emptor). The 10/01/2020 RTU 4.2 is a good enough straight swap battery - lifestyle [infrequent daily use] is the killer of all starter batteries on GV's including big Odessy 100+ aH 1000+CCA. Crap handbrick and left clog position are original poor design engineering translations petrol/CDR and LHdrive/RHdrive. Manuals here, Best of luck.