The only purpose for the resistor is to simulate a fully-charged battery to do the final voltage setting. The simple substitute is- - - -surprise- - - -a fully-charged battery! As the internal resistance of the battery increases, the generator output tries to rise to continue putting current into the battery. The 1/4 ohm resistor in series with the charge current drops the current sufficiently to get an accurate adjustment of the voltage. I use a 6 volt sealed beam headlight with both high and low beams wired in parallel to simulate the resistor, and wire it between the BAT terminal and the ammeter to do a final adjustment. BTW, I started servicing DC generator charging systems in the early 1960's so this is actual experience talking, not a quotation from a service manual.
Starting out- - - -adjust the closing voltage. With the engine idling VERY slowly, like 400 RPM or so, the cutout relay points should be open, and the voltage at the armature will be below 6 volts. S-l-o-w-l-y raise the RPM and watch the voltage. The cutout should close at about 6.5 volts or slightly above. If the regulator has been adjusted properly for the 8 volt battery, the closing voltage will probably be 8.5 volts or so. Drop the spring tension on the cutout points to get the 6.5 volt setting. Don't go below 6 volts, for reasons I'll cover shortly. The next setting is the current relay, the coil behind the Armature wire. Put a heavy load on the electrical system such as high beam headlights, heater blower, brake lights, radio, and anything else you can turn on. The idea is to make the generator produce maximum current. Adjust the current regulator to 30-35 amps with the engine at a fast idle, 1500 RPM or more. Shut down the "load" circuits and proceed to the voltage regulator setting. Final adjustment- - - -attach the inline resistor (headlight) between the battery wire and the BAT terminal on the regulator, fast idle again, and adjust the voltage regulator coil (behind the field wire) to 7.5 volts. Be aware that putting the cover on the regulator will lower all the settings slightly, so carefully check all your settings by placing the cover on the regulator after each adjustment. To get an accurate measurement, cycle the current and voltage regulator points several times by pushing the points open and allowing the cutout relay to cycle. Be careful not to short anything out while removing and replacing the cover during the adjustment procedure!
Final test- - - -drop the RPM back to the S-l-o-w speed, and be sure the cutout relay opens every time the armature voltage drops below 6 volts. If it doesn't, the battery reverse current will make the points stick, and the battery will discharge itself through the generator. Good luck!
Jerry
