The accessory circuit consists of your battery, ignition switch, a STSP switch and accessories such as an electric PTO, Headlights, Taillights, etc. When your ignition switch is in the “run” position your accessory terminal is energized by the battery. Power then runs from the “A” or accessory terminal to a STSP (Single Throw Single Position) switch. This switch is wired in-series and is a way to connect and disconnect power to your accessory such as your headlights. Your headlights are then wired to the STSP light switch and are wired in parallel to each other. This means two wires will come from your light switch and connect to each headlight individually. Two ground wires will also come off each headlight individually and connect to the common ground. If you were to wire your headlights in series each headlight will only use 6 volts rather than 12 and the brightness will be diminished.
A circuit is a closed loop of wiring and components beginning at the positive side of the battery and ending back at the negative side of the battery. This loop is often closed using a common ground. Electricity only flows when a circuit is a closed loop. If the loop is open no electricity flows.
You can determine the amount of current being used and charged on your tractor’s system by placing the meter in-series with the circuits of the tractor. To do this: first remove your red probe and plug it into the 10 amp Max port on your DMM. Then set your DMM to DC Current with the range of 10 amps. Now you unplug the wire going to your ignition switch’s “B” terminal. By clipping alligator clips to your DMM probes you can now connect one probe to the “B” terminal of your ignition switch, and your other DMM probe to the wire that normally goes to “B” terminal on the ignition switch. Now when you run your tractor the current will flow through the meter and your DMM can give you a reading. It will tell you how many amps are flowing through your system.
A common ground is a path for electricity to flow back to the negative side of the battery. Most systems use the conductive metal on the engine block and tractor frame to lead electricity back to the negative side of the battery.