Automotive wiring 101

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Before you start running circuits, it is best to know how much amperage each one of those accessories will take to power it up. Keep in mind there are four types of accessories we will be dealing with; un-switched continuous, un-switched intermittent, switched continuous, and switched intermittent.  
 
Before you start running circuits, it is best to know how much amperage each one of those accessories will take to power it up. Keep in mind there are four types of accessories we will be dealing with; un-switched continuous, un-switched intermittent, switched continuous, and switched intermittent.  
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To follow this through, let’s look at a typical 1960/70 automobile and see what kind of amperage we are dealing with and how they relate to the design of an automotive electrical system:
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1. Headlights. There’s four, and when on high beam the 'typical' amps each is 5A for a total of 20A.
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2. Taillights. There’s four and at .7 amps each , plus the license plate light, =3.5A.
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3. Brake lights. Four @ 2.25 each, = 9A.
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4. Dash lights. Four @ .3A each, =1.2A.
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5. Emergency flashers. When your flashing, the four brake lights at 2.25A each, two dash indicator lights at .3A each, plus front turn lights at 2.25 each, =14.1A.
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6. Interior lights. One overhead light and two door sill lights, =1.8A.
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7. Back-up lights. Two at 2.25A, =4.5A.
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8. Lighter. 16A if you actually have a lighter, even if used as a power-point, = 16A
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9. Horns. Two at 6A each, =12A.
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These add a total of 82.1 amps. These are not all continuous, so you don't need 81 amps all the time. Your continuous loads are only items 1, 2, and 4 as a general rule, so the continuous load is only 35.5 amps, less than half.
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To calculate for switched circuits:
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1. Ignition, 12A.
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2. Wipers, 6A.
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3. Turn signals, 7A.
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4. Heater/AC, 24A.
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5. Gauges, 4A.
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6. Radio, 7A.
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7. Power seat, 16A.
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8. Power windows, 16A.
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The total load equals 92 amps, but your continuous load is lower. Items 1, 2, 4, 5, 6 are continuous and total 53 amps.
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Just adding up 'basic' continuous loads (35.5 and 53), equals 88.5 amps for total continuous load. This number represents how many amps your charging system needs to put out just to stay even, so as not to create a draw on your reserve, the battery. Normally, for sizing the charging system, the intermittent loads won't count; you draw off the battery and then the charging system will replace the power as you drive.
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As you advance your ride with the latest electronic features, you have to take into account the extra power that the electrical system must generate to keep up with your accessories. Perhaps, that new electric fuel pump and twin fan setup will become the cause of the dreaded ‘Dead Battery Syndrome’ that is plaguing the automotive scene today. The old 63 amp GM alternator will be tossed for a 140 or even 200 amp alternator in order to run that giga watt stereo system that you’re cruising with today. Do your homework and build your electrical system right!
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===Grounding===
 
===Grounding===

Revision as of 13:56, 19 September 2014

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