mtflyboy25

So you want to wire yourself a new accessory on your hot ride? Well make sure it is wired correctly!

First off we need to understand a couple of things.


1. The more power the device takes, the more amps it draws, the bigger wiring you need...

2. The longer the wiring is to the device the more amps it draws, the bigger wiring you need...

3. The ground side of the accessory takes the same size as the input because what comes in goes out... Get it?

So first off we need to find out how many amps your device will draw...

How to Measure Amperage in a system:

1. Buy / Borrow / Use a digital multimeter....

2. Turn on the digital multimeter. Most digital systems run a self-check before they are ready for use. Allow a minute for the meter to complete its testing...

3. Set the function selector to read amps from battery power or alternating current. The function setting "A~" measures alternating current in amps, or AAC; "A=" measures direct current in amps, or ADC. Use A=...

4. Set the range so the maximum is well above the highest reading expected. This will protect the meter from getting overloaded. If you overshoot the range and cannot get a reading, set it lower.

5.Connect the leads to the proper terminals for measuring current. Connect the black lead to the "COM," or common terminal. Connect the red lead to a terminal marked for low- or high-current measuring. The low-reading terminal may be identified as "300mA." This would give readings in milliamps; 1 milliamp equals .001 amps. Multiply by 1,000 to get the figure in amps.

Example:



6. Break into the circuit to measure its current. Set the red probe on one open end and the black probe on the other. This may require cutting a wire to get the probes between the circulating current. The idea is to let the current flow through the digital multimeter to allow it to get a reading.

OR

Use a spare wire of good thick gauge I usually use 14 AWG or 12 AWG wire for testing purposes. Follow the picture below...




You will get a reading now... If it is negative switch the leads you are using around, red should be the closer to the battery on the wire and black should be closer to the device.

Now you will get a reading most likely between 0 and 50 amps.

For example here was my list of things I tested...

I looked at the highest number the meter showed from begining to end. Some devices take more juice to start like an electric fan, then they will settle into a continuous stable power draw...

Example List:

Stereo Turn on = 0.03 amps continuous
Fan = 9.00 amps Max Start, 4.76 continuous - makes sense it takes more juice to get it moving...
Fuel Pump = Max of 8.7 amps with and without car running/revving...
Gauges power and turn on = 0.75 amps start up, 0.7 amps continuous
Each little light alone when switches on adds 0.02 amps continuous.....

Now with this information you can decide what size of wire you need.

Here is a chart showing the max power a wire can handle before degrading and then 80% which seems to be a recommend percentage of the max to use continuously.



Now looking at my numbers and the chart I could get away with using a 21 gauge wire for my fan. But I prefer to go safe so I would use a minimum of 19 gauge wiring. Now you are probably thinking that is really small! You are correct, which is why I dont go smaller than 18 gauge wiring. It is easier to use and wire together using crimp connectors or soldering.

Let me know if you have any questions!