Normally and originally if it had the LHBD switch that controlled the Low or High charge rate and there was only a 2 terminal (a few had 3) Cutout Relay on the genny instead of a full fledged VR. The gennys FLD wired up to the LHBD and the gennys ARM wired to the cutout realy
I only saw 2 terminals and only one relay/coil on that box (would make it a Cutout Relay NOT a Voltage regulator). Id say the wirewound resistor you show is for the cutout relays shunt......
Its very important that BOTH the Genny and Relay PLUS the LHBD switch have good clean bright shiny to case frame grounds.
When shes running dead ground the gennys FLD post (NOT the post to the relay, thats the ARM post) n see if she charges then?? If so but NOT otherwise, the wires bad from FLD up to LHBD switch,,,,,,,or LHBD has a bad ground,,,,,,,or perhaps the LHBD field current resistior is bad/open, but even it were and it had a ground it could still charge cuz that field resistor is ONLY used for Low (L) charge.
A good 6 volt battery ought to read 6.3 volts when setting but when the tractor is running at fast RPM a good charging system takes the voltage to 6.5 to the 7 range.
WORK THROUGH MY TROUBLESHOOTING PROCEDURE