Upfitter switches
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Senior User
Joined: Apr 2008
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Upfitter switches
im installing a 20 inch rigid light bar to my truck and was wondering what switch is best to run the light bar off. I know that aux 1 and 2 are 30 amp, aux 3 is a 10 amp and aux 4 is a 15 amp. im just not sure what one I should hook the bar up to. I don't want to over or under power the light bar. also I need to hook up 3 1/2 inch lights that came with my smittybilt bumper and they are 55 watt 12 volt lights. what upfitter switch should I hook those lights up to. any insight would be great thanks
Junior User
Joined: Mar 2010
Posts: 67
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From: Tucson
Electrical formulas
What is the power rating on the light bar?
Here are a couple of real easy formulas you can use to find out about about your loads...
Eq. #1) P=I^2*R
Eq. #2) V=I*R
Where P is power (watts); I is current (amps); V is potential (volts); R is resistance (Ohms). Since in accessories we rarely talk about resistance, we solve Eq. #2 for R --> R=V/I and then substitute this new version of Eq. #2 for R in Eq. #1 which gives us P=I^2*V/I or simplified P=I*V. So when you know power (55watts) and voltage (12volts) as in the case with your lights, and you want to know how much current they'll draw, you just solve our new version of Eq.#1 for I, it looks like this I=P/V, then simply plug in real numbers and viola or in other words "whaaalaaa"
I = 55/12 --> I=4.6 amps
For your light bar replace the 55watts in the equation with whatever the light bar's power rating is and calculate.
Here are a couple of real easy formulas you can use to find out about about your loads...
Eq. #1) P=I^2*R
Eq. #2) V=I*R
Where P is power (watts); I is current (amps); V is potential (volts); R is resistance (Ohms). Since in accessories we rarely talk about resistance, we solve Eq. #2 for R --> R=V/I and then substitute this new version of Eq. #2 for R in Eq. #1 which gives us P=I^2*V/I or simplified P=I*V. So when you know power (55watts) and voltage (12volts) as in the case with your lights, and you want to know how much current they'll draw, you just solve our new version of Eq.#1 for I, it looks like this I=P/V, then simply plug in real numbers and viola or in other words "whaaalaaa"
I = 55/12 --> I=4.6 amps
For your light bar replace the 55watts in the equation with whatever the light bar's power rating is and calculate.
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