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Discussion Starter · #1 ·
Planning to rewire my fog and driving lights soon and I want to use a relay in place of the direct wire to the inside fuse block that I have now. My lights did not come with relays and are tied directly to 12 VDC line at the fuse block per the directions in the lights.

Two questions:

1. Which relay from radio shack is suitable for this?

2. Where do I find a 5 VDC circuit to power the relay?
 

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A standard automobile relay (which can be found under the hood of many junkyard cars for free) runs at 12v, and will be perfect for your needs.

On the relay there is either 4 or 5 pins. You want a 4pin relay.

On the bottom you will see numbers by the pins.
Pin 30 is power out to the lights.
Pin 85 is ground
Pin 86 is signal, such as from a switch on the dash
Pin 87 is power in, from the battery

Run to the junkyard, grab a few Bosch relays, head to the parts store and get some wire and female spade terminals. Assemble and enjoy brighter lights.
 

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Discussion Starter · #3 ·
Thanks theconstantevolution,

I'll see what I can find. Question still stands though, With a car relay, what voltage is needed from the switch, and where is a good place to tap into to get it?
 

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All relays for auto are 12v all the way around. Power in/out, switch.

As for feeding your relay, I would tap the parking lights. Feed that to a switch, then run from the switch to the relay. The reason I recommend this way is because you normally don't use fog or driving lights unless your other lights are on as well, and this would make it so you don't accidentally leave them on when you shut everything thing off.
 

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You don't need any more than 6V to turn most relay's "on". So you can tap into a solid power source for your switch than run the other side of the switch to the "signal" post of the relay. You can either run a power line directly to the battery (my choice) or tap into something else. I say the other way so you're not pulling on anything else to power your lights. Either way you can tap into a true ignition source for the switches power that way you won't run the lights unless you turn the key, but your relay will still have solid power for it's job.
 

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You don't need any more than 6V to turn most relay's "on"
When is the last time Isuzu made a vehicle with 6 volt power system? Dont confuse the poor guy.

As for feeding your relay, I would tap the parking lights. Feed that to a switch, then run from the switch to the relay. The reason I recommend this way is because you normally don't use fog or driving lights unless your other lights are on as well, and this would make it so you don't accidentally leave them on when you shut everything thing off.
This is how I always wire mine. I killed a few batteries by leaving driving/fog lights on before I started wiring into the parking lights.

I say the other way so you're not pulling on anything else to power your lights.
The only thing that will be drawing power from another circuit will be the coil of the relay which pulls less then .10 amps. You can run a bunch of them on the same circuit with no issue.



Where that drawing says "low beams" to wire into the switch I connect to the parking/tail light circuit instead.

Any auto parts store has lots of relays if you dont mind paying a little bit for one and dont want to go the junkyard. Make sure it can handle at least 20 amps on the contacts, most do and are usually 30 amps.
 

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Discussion Starter · #7 ·
Thanks guys. I appreciate the info.

I wonder if the same setup would work for a scooter lift gate for my mobility scooter... I've already got a power line from my hitch wiring that I'm not using. I'll have to give it a try when I get the lift.
 

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Gizmo42 said:
You don't need any more than 6V to turn most relay's "on"
When is the last time Isuzu made a vehicle with 6 volt power system? Dont confuse the poor guy.

As for feeding your relay, I would tap the parking lights. Feed that to a switch, then run from the switch to the relay. The reason I recommend this way is because you normally don't use fog or driving lights unless your other lights are on as well, and this would make it so you don't accidentally leave them on when you shut everything thing off.
This is how I always wire mine. I killed a few batteries by leaving driving/fog lights on before I started wiring into the parking lights.

I say the other way so you're not pulling on anything else to power your lights.
The only thing that will be drawing power from another circuit will be the coil of the relay which pulls less then .10 amps. You can run a bunch of them on the same circuit with no issue.



Where that drawing says "low beams" to wire into the switch I connect to the parking/tail light circuit instead.

Any auto parts store has lots of relays if you dont mind paying a little bit for one and dont want to go the junkyard. Make sure it can handle at least 20 amps on the contacts, most do and are usually 30 amps.
I wasn't trying to confuse anyone, just trying to answer his Q. He asked what voltage he needed and I was trying to tell him he had more than he needed...guess I should have just said that.

Thanks for answering him more clearly, I'm sure your answer helped a bit more than mine did...lol
 

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Discussion Starter · #10 ·
Yeah it does, but they are few and mostly connectors.

Here's a different question.

If it doesn't matter if I use either 5 or 12 volts to activate the relay, why use it at all as the lights are already connected to 12 volts at the switch?
 

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the relay is your "contact" to supply 12v to your lights.
w/o a relay your "contact" is the switch.
Most switches are only rated for 10-15 amps where as a relay is normally 30 or 40 amps.
Every notice that your switch gets hot?switches burn out and or melt if they have alot of amps going through them.
So you can use a small switch to "turn on " the relay less than 1 amp and then the relay will carry up to the rated capacity better than a switch will

55w light / 12v=4.6 amps
so 2 55w lights will push almost 10 amps so the switch will overheat and be at capacity and prone to fail by melt down or fire
 

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order from allelectronics.com You can get a whole bag of relays for what radioshack would charge for one.
 

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Discussion Starter · #14 ·
stusvend said:
order from allelectronics.com You can get a whole bag of relays for what radioshack would charge for one.
Which part number would you suggest? It seems to me that RLY-455 would be the one to get. Not a bad price at $2.25 each.
 

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Junkyard is FREE.99 >:D

Haven't had a junkyard relay fail yet. At least not an OEM one. I've had a couple "aftermarket" relays from kits fail on me though.
 

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Discussion Starter · #18 ·
Guys,

I've wired manufacturing machinery in factories to 240V, 100Amp 3Ph circuits using 4AWG wire. I think I can run the wires to my fog lights using either 16 or 14AWG. In fact, Ive got the wiring for the battery to switch connection that came with one of the light sets that I never used because I originally wired them directly to the fuse panel inside the cab.

Neither set came with relays though, and hence this thread.

What I'm asking about is the part number of the relay to use should I opt to buy new ones rather than JY ones for the best results. I've heard far too many horror stories of cars burning up in the garage due to faulty relays and or circuit breakers.

True, most of those stories are about Fords, so I'm guessing that its wise to stay away from any relay used in a Ford.

My plans include the use of a NEMA 4X enclosure to house the relays and their connections that will be mounted in the engine compartment. Also the addition of a third circuit for a wheel chair lift to be mounted to the tow hitch and wired to a switch inside the cab so I can carry my scooter with me but still be able to turn the power off when the lift is not on the truck since I can only think of two or three times a year when I will need it.
 

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As a Ford guy I can tell you the weak point in Ford wiring (at least old Fords) was that they used to run the lighting through the headlight switch without relays, much in the way your lights are now, as well as running massively undersized grounds.

A relay such as this

http://lh3.googleusercontent.com/public ... qHfQI8acvA

though you need a 4 tab, not a 5 tab. The middle tab is unneeded for your application.
 
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