There are many competing charts online indicating what current is allowed with various gauge wires. Maximum current ratings are to prevent the insulation on the wire from breaking down or melting due to overheating. When bundled together, the maximum rating must be reduced to account for the decrease in heat dissipation. Below is a conservative listing of the maximum current for typical wire gauges, but even these maximum ratings must be reduced under various loading conditions.

Fusing of circuits is also a concern. This quotation makes the point:

First, fuse ratings can be a bit misleading. A 10A ATO (automotive) fuse will conduct 11 amps for 100 hours minimum. At 13.5 Amps a 10A ATO fuse can take as long as 10 minutes to blow. It is not like once you draw 10 amps “poof” the fuse is gone. (From FUSE SIZING PRIMER located at http://www.powerlet.com/learningCenter/fuseSizing)

In general, for 12v wiring (13.5v source) where the length of the point-to-point runs (which equals 1/2 of the full circuit back to ground) are as follows, this rule-of-thumb chart is useful (max 3% voltage loss):

• Contact resistance is the resistance to current flow (due to surface conditions and other causes) when contacts are touching one another ¹⁾and it is the main ingredient in the electrical contact reliability.
• Electrical connections represent the weakest parts along an electrical wire chain. The main reason for these connection failures is contact resistance between the elements of connection.
• Contaminations (usually dust, found inside or outside the electric connections), films on the surfaces of contacts and increased humidity lead to an increase in corrosion, contact temperature and contact resistance of the joints. These contaminations can be due to surface oxidation, dust deposition and corrosion of contact material. The increase in contact resistance is generally attributed to corrosion film growth. So, the contact reliability is greatly degraded and contact life time is greatly reduced.
• Copper, like all other common metals, readily develops a very thin surface oxide film even at ordinary temperatures when freely exposed to air. The most widely used coating materials are tin, silver, cadmium, and nickel. Compared with uncoated copper connections the nickel and silver coating of copper connections show excellent stability and low initial contact resistance. Contact resistance between the connected joint elements causes unequal distribution of currents in the upper and lower joint parts. Therefore, there will be higher power losses at the joint ends, hence higher temperature. This higher temperature leads to an increase of the contact resistance at the joint ends.
• Contact resistance may be divided into three major components:
  • Resistance of the basic metal.
  • Resistance due to the converging of the lines of current flow as they pass through the small area (true conducting area) of the joint (constriction resistance).
  • Resistance resulting from surface tarnish films (oxidation films), trapped between the members of the joint, frequently called as film resistance which is affected directly by the environment (temperature, humidity, vapors, dust, etc.).
• Operating and maximum temperature: The current carrying capacity of a wire connector is usually determined by the maximum temperature at which the connector is permitted to operate.
  • The rate of surface oxidation in the air of conductor materials increases rapidly and may give rise in the long term to excessive local heating at joints and contacts.
• Contact clamping force: Increasing the clamping force leads to a decrease in the contact resistance.
  • The continuous increasing of the clamping force improves the performance of the contact joint, but if it exceeds a certain limit, the contact spot would be damaged and so the contact resistance will be higher, i.e. a bad contact performance. This limit depends on the kind of joint material and its hardness. Generally, the life time of the contact increases by increasing the clamping force.
  • A good example of clamping force gone wrong is when two wires are twisted together tightly to begin with and slowly loosen through heat and/or use which can begin the degradation of the circuit.
• Increasing the load current increases the power loss which appears as heat. Thus, the increase of the load current decreases the life time of the joints. The life time of the joints decrease with the increase of the operating temperature. ²⁾Connectors can “fry” because their contact resistance is too high, creating a voltage drop across them. The heat created tends to increase the resistance, and the result is more voltage drop, thus more heat.
• You cannot lower the contact resistance of two metal contacts by applying a nonconductive grease to them. ³⁾

DC Rule of Thumb - For those switches that list an AC voltage rating only, the “DC Rule of Thumb” can be applied for determining the switch's maximum DC current rating. This “rule” states the highest amperage on the switch should perform satisfactorily up to 30 volts DC. For example, a switch which is rated at 15A 125VAC (10A 250VAC), will be likely to perform satisfactorily at 15 amps up to 30 volts DC (VDC). Depending on the load, it's sometimes best not to exceed 15VDC, for these switches.

AC or alternating current is an electric current or voltage that reverses its direction of flow at regular intervals and has alternately positive and negative values, the average value of which over a period of time is zero.

DC or Direct Current is an electric current or voltage which may have pulsating characteristics, but which does not reverse direction. It's potential is always the same relative to ground, and it's polarity is either positive or negative. A battery is one example of a source of direct current.

Types of Loads

An electric load is the amount of electric power delivered or required at any specific point or points on a system. The requirement originates at the energy consuming equipment of the consumers. More simply put, a load is the piece of equipment you turn on and off.

Resistive loads primarily offer resistance to the flow of current. Examples of resistive loads include electric heaters, ranges, ovens, toasters, and irons. If the device is supposed to get hot and doesn't move, it's most likely a resistive load.

Inductive loads are usually devices that move and normally include electric magnets, like an electric motor. Examples of inductive loads include such things as power drills, electric mixers, fans, sewing machines, and vacuum cleaners. Transformers also produce inductive loads.

High Inrush loads draw a higher amount of current or amperage when first turned on, compared to the amount of current required to continue running. An example of a high inrush load is a light bulb, which may draw 20 or more times its normal operating current when first turned on. This is often referred to as lamp load. Other examples of loads that have high inrush are switching power supplies (capacitive load) and motors (inductive load).

Information from Carling switches was used as a succinct description of the basics ⁴⁾.

If you would like to do further research into switch ratings, search for the Eaton (Cutler-Hammer) Switch Training Manual ⁵⁾.

It's possible to use a volt/ohm meter, or Digital Volt Meter (DVM), to check the resistance from any ground point on the bike back to the negative battery terminal. Such resistance checks can discover problems. To do this type of check, the meter is set on a low resistance scale (less than 100ohms if possible). The negative battery cable should be removed from the battery (to disable power on the bike). One lead of the meter is placed on the battery end of the battery cable (now disconnected from the battery) while the other end is placed on the ground point being checked. If properly connected, the meter should read a very low resistenace, nearly ZERO (usually less than one ohm).

A quick and dirty test (although not able to detect borderline issues) can be performed with a powered test light connected between the battery cable and the ground point under examination. If the light illuminates, there is a circuit connection between the two points.

There is another method for testing grounds. You can test ground connections using voltage checks. This uses the voltage setting of the meter and does not require you to remove the battery cable. With this method, you will use the battery itself to test for continuity to various ground points on the bike. A DVM is perferred for this method.

First, set your meter to read DC voltage where 12 volts is easily measured (maybe the 20v scale or close to that). Place the red lead from the meter on the positive battery terminal. In fact, you should find a way to clamp it on that terminal (maybe using a plastic clamp). Be very careful not to short the positive terminal to any part of the bike. Now place the black lead on the negative battery terminal to take an initial voltage reading of the battery itself. This voltage should be close to 12.8 DC volts. Whatever your voltage reading, directly on the battery, will be called the REFERENCE VOLTAGE.

When checking the voltage between the positive terminal of the battery and ANY GROUND POINT on the bike, you should have a voltage reading very close to the Reference Voltage (like 12.8v above). Every single ground point on the entire bike should measure within .3v of this reading.

So, if you take the black lead to the other end of the negative battery cable, on the Powertrain Ground, it should measure very close to the Reference Voltage. If you take the black lead to the ground pin on the headlight connector, it should measure very close to the Reference Voltage. If you take the black lead to the ground pin in the taillight connector, it should measure very close to the Reference Voltage. If you take the black lead to the cylinder heads (next to the spark plugs), the meter should read very close to the Reference Voltage.

IN EVERY CASE, the red lead is still on the positive battery terminal and the ground point you are testing should have a good connection back to the negative battery terminal through the ground connections of the wiring harness, the Powertrain Ground, the frame and the battery engine case ground point. If ANY GROUND POINT does not measure within .3v of the Reference Voltage, there is something loose, frayed, corroded or disconnected. ⁶⁾

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