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Old 02-20-2011, 14:16   #1 (permalink)
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Need help figuring wiring / accessories needed for off road light install

I need help figuring out what relay i will need for an off road lights install for my 2003 Ford Expedition

Here is what I have ordered so far:

(4) 100 watt General Electric 4537 200,000 candlepower sealed beam bulbs

(4) Grote Par 46 Rubber Housings

(1) N-Fab Light Bar for 2003 Ford Expedition


Here is what I want to use for wiring them:

10 gauge wiring

So with (4) 100 watt bulbs, that's 400 watts divided by a 12 vdc system = 33.3 amps, so I will get a 40 amp fuse to handle between 30-40 amps.

I will also use a 40 amp relay but how do I figure out what ohm rating it should be?

The www.12volt.com ohm's law resistance calculator says the following:

400 watts (power) divided by 33.3 amps (current) is .36072 ohms. So how do I figure the resistance rating of the relay I need with the number .36072?
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Old 02-20-2011, 15:17   #2 (permalink)
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Re: Need help figuring wiring / accessories needed for off road light install

When a relay closes the contacts, there's no resistance. It's a direct connection so there should be no resistance in the circuit.
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Old 02-21-2011, 02:05   #3 (permalink)
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Re: Need help figuring wiring / accessories needed for off road light install

as stated no need to know resistance for it just get a 40 amp relay all should be ok.

Ian
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