English 
how do you connect a voltage and current gauge to a boat
Boat voltmeter: For the battery voltmeter , observe whether the pointer is at the "zero" mark . If not , adjust the zero button to adjust the pointer to "zero" first . The voltmeter must be connected in parallel with the measured electrical appliance , i.e. connected to the two ends of the measured electrical appliance . The current must enter from the positive electrode (red terminal) of the voltmeter and then flow out from the negative electrode (black terminal) . To estimate the voltage , select a suitable range , which must be greater than the test voltage .
Boat ammeter: Before measurement, check whether the pointer of the ammeter is aligned with the "0" mark. If it is not aligned, adjust the "zero adjuster" to make the pointer return to zero. During measurement, the ammeter shall be connected in series to the low potential side of the circuit under test. The current should flow in from the "+" terminal (red terminal) and out from the "–" terminal (black terminal). Estimate the current and select the appropriate range . The measured current shall not exceed the range of the ammeter .
The two wires from the battery are positive and negative, and the positive and negative of the voltmeter are connected correspondingly . The ammeter can be connected in series on a wire (no matter which one) to the motor . Voltmeter parallel battery, ammeter series battery. If you modify the car, such as overpressure , it is still very useful Because the original undervoltage protection value changes after the overpressure, the voltage and current value of the motor under the extreme speed state after the overpressure can also be seen , so as to judge whether the most economical and ideal energy-saving state is reached, with high power consumption and low efficiency .
A boat meter gauge can only be connected to the battery to show the swing you want , that is , the positive electrode is connected in series , but an ammeter can only be connected in series, which is unheard of and connected . If it is connected to other places , it seems that the situation you said cannot be met, and an ammeter cannot meet your needs. You can install a voltmeter that should meet your needs .
Get a Quote / Info