# add-a-fuse in engine bay fuse box for 12v switch...



## patatewz (Aug 18, 2012)

Hi,

I need to add-a-fuse 15 amp in the fuse box in the engine bay (not the fuse box in the car driver side).

I need a 12 v source when i turn the key to on. I dont want a 12v always on...

Anyone can tell me where i can add my add-a-fuse?

Thanks.


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## sciphi (Aug 26, 2011)

I wonder where the emergency brake switch leads, as that switch triggers the DRL's on when the e-brake is released. The DRL's only come on when the engine is on and the e-brake is released. 

What about setting up a fused relay system running off the battery? The relay will trigger on whenever the e-brake is released, and activate whatever it is you're running (guessing the meth system).


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## Jthod (Jul 15, 2012)

The test light is your friend. Using a fuse, probe any empty fuse ports while cycling the key. Tapping into the cigar lighter would also work. Just make sure it's fused correctly to handle the amperage you are using.


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## patatewz (Aug 18, 2012)

hmm i found many empty fuse not use in the fuse box but no one with power in there... i think its far to go in the car to power up un external pump...


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## patatewz (Aug 18, 2012)

i like the idea of the relay can you explain me a little more about how i can install a relay? maybe a link on a generic how to or what i need to buy to make it. for now i have only a add a fuse nothing else...


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## XtremeRevolution (Jan 19, 2012)

patatewz said:


> i like the idea of the relay can you explain me a little more about how i can install a relay? maybe a link on a generic how to or what i need to buy to make it. for now i have only a add a fuse nothing else...


To install a relay, you must first understand how one works. Do you understand how a relay works?


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## patatewz (Aug 18, 2012)

its like a remote switch ? i can take my source directly on my +batterie but i past via a relay so its turn on only when i turn the key on and the relay is connect to a switched source but my pump dont take the curent from this source.

that it?


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## sciphi (Aug 26, 2011)

Basically the relay handles the heavy-duty, high-current loads. It's used to supply lots of power to electrical devices without running all the power through a regular switch that can't handle lots of electrical current. 

Look through the headlight harness threads on here, especially the ones that I and XtremeRevolution have posted. Those should explain relays a little more, and why they're good to use for running high-powered pumps and lights.


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## patatewz (Aug 18, 2012)

im french sorry for my very bad english...


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## Jthod (Jul 15, 2012)

here's a simple schematic. Replace the VCM input to the relay, with an ignition voltage signal (cigar lighter), and fuel pump with meth pump, etc..


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## XtremeRevolution (Jan 19, 2012)

I'll explain it as best as I can. 

A relay has an internal switch that allows you to switch power on and off to a high-current wire, without needing a high-current switch. You can use a generic switch to open and close the relay, that will open and close the source of the high current. 

Say you wanted to switch a 15-amp circuit on and off. Without a relay, you would need a large switch capable of supporting a 15-amp load. With a relay, you can use as small of a switch as you would want, and the relay will serve as the high-current switch. The small switch that you control is simply a trigger for the high-current switch inside the relay. 

See this site for more information: 

HowStuffWorks "How Relays Work"


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## Jthod (Jul 15, 2012)

I guess I would have just linked wikipedia...


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## patatewz (Aug 18, 2012)

yes i understand all this. But what i need to know is how we install it in a cruze or a car and what i need to buy  but for the basic its how i figured it work. thanks a lot for the information it confirm my idea but i need a little more pratic information.


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## sciphi (Aug 26, 2011)

At its simplest, you'll need enough wire to reach wherever you need to go, a relay, some spade terminals, some ring terminals, a good crimper (if you can't solder), heat-shrink, and some wire loom to make it all look pretty. Some electrical tape helps, too. 

I'd recommend 14-gauge wire for the power and feed wires, and 18 gauge wire for the signal wire and its ground.


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