If your '39 is like my '37 my comments may help. If not, I will probably confuse you even more.
The harness that you have probably requires you to move the generator cut out to the generator where it belongs. The cut out is essentially a diode that prevents current running from the battery to the generator, turning it into an electric motor when the ignition is on but the motor is off or idling. The field resistance will be located on the body of the light switch. This resistance is bypassed when the light switch is pulled to the first stop (used when there is heavy current demand for heater/radio). The next stop of the switch is for parking lights which also bypasses the resistor, as well as the third and final stop for the headlights. If you don't have such a light switch then none of this is true, such as a later generic switch with the normal off/park/headlight stops.
The ammeter should have a fuse on the body of the gauge. This is your only fuse unless you have placed in line fuses for heater, etc.
By modern standards, or even standards of the late 40s, this system seems archaic. You actually have to look at your ammeter when driving and pull the light switch to the first stop if you are doing stop and go driving or using the radio or heater. On the first stop, no lights come on, you are just bypassing the resistor. Also, if you drive for hours at highway speeds, to keep from overcharging the battery you may want to drive with your lights on. I find this rather charming and part of the character of these older vehicles.
Kent
Last edited by Lightholder's Dad; 07/15/2021 12:26 AM. Reason: clarity
