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Do i need a relay?

Old 04-19-2017, 10:41 AM
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Default Do i need a relay?

If im running some old school kc type lights do I need a relay or can I wire it straight through the switch. Also, are yall using a premade harness or are you bulding as you go? Got some TJ factory lights and some baja offroad lights for dirt cheap.
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Old 04-19-2017, 12:34 PM
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I recommend a harness. Anything stronger than stock lighting is probably going to burn your switch up. Even upgrading your harness with stock lighting increases light output.
As far as buying or building a harness is up to you. If you have wire and relays laying around I'd say build. Just as easy to buy one online for 20-30 bucks.
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Old 04-19-2017, 01:04 PM
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For something like that id definitely run a relay. Those oldschool halogen KC lights pull some decent amperage.
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Old 04-19-2017, 01:21 PM
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To clarify, it will be independent of the stock lights, just was curious as to whether most built their own harness or bought one. As for the relays, I have a few laying around. Is there any specific kind I need?
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Old 04-19-2017, 01:32 PM
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Originally Posted by JSJJ388 View Post
To clarify, it will be independent of the stock lights, just was curious as to whether most built their own harness or bought one. As for the relays, I have a few laying around. Is there any specific kind I need?
i'd calculate how many amps your lights draw and go from there.

Amp draw is a simple mathematical calculation. Divide the total number of watts by the system's volts. For example, a 100-watt bulb in a 12-volt system will draw 8.3 amps.
(100w / 12v = 8.3a)
so let's say you have 4 100w lights running on a 12v system, that would be about 34 amps, so a 40A relay will work. if it draws closer to or above 40A, use 2 relays, a 4 pin and a 5 pin and use the 87a bridge so all the lights turn on with one switch.
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Old 04-19-2017, 01:37 PM
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@Cane, since you seem to know what youre talking about with electrical and I dont lol.


My plan is to put the two TJ fog lights on my bumper somewhere and run them to one switch.

Then put the 4 baja lights on the roof and run the outside two on a switch and the inside tow on a switch so that I can run 2 or 4. So one relay per switch should be adequate, correct?
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Old 04-19-2017, 02:30 PM
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yes, so basically if your fog lights are independent from your baja lights, you'll have 3 4-pin relays, each activated by a switch.

here's a basic example of the wiring (for one relay), using an on/off switch

86 to ground
30 to the 12v source (battery)
85 to switch (your switch needs to transmit a signal to the relay, so it must be wired to a 12v source too)
87 to the load (your lights)




that means that when you flip the switch on, the coil energises and connects 30 and 87 together, making the current go straight from the battery to your lights, through the relay instead of the switch. do that x3 and you should be good to go.

Last edited by Cane; 04-19-2017 at 02:34 PM.
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Old 04-19-2017, 02:52 PM
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Originally Posted by Cane View Post
yes, so basically if your fog lights are independent from your baja lights, you'll have 3 4-pin relays, each activated by a switch.

here's a basic example of the wiring (for one relay), using an on/off switch

86 to ground
30 to the 12v source (battery)
85 to switch (your switch needs to transmit a signal to the relay, so it must be wired to a 12v source too)
87 to the load (your lights)




that means that when you flip the switch on, the coil energises and connects 30 and 87 together, making the current go straight from the battery to your lights, through the relay instead of the switch. do that x3 and you should be good to go.
Man I love this forum. Thanks!
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Old 04-19-2017, 02:54 PM
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Any thoughts on where to locate the switches? Im thinking on the front face of the center console. Also, can I just run a single 12v and tie it into all 3 switches?
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Old 04-19-2017, 04:22 PM
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Originally Posted by Cane View Post
86 to ground
30 to the 12v source (battery)
85 to switch (your switch needs to transmit a signal to the relay, so it must be wired to a 12v source too)
87 to the load (your lights)
You could also run 12v to 30 and 86 and make 85 a switchable ground. Sometimes I use this method for cooling fans etc because if the switch shorts out the device just stays on.
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Old 04-19-2017, 04:26 PM
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Originally Posted by JSJJ388 View Post
Any thoughts on where to locate the switches? Im thinking on the front face of the center console. Also, can I just run a single 12v and tie it into all 3 switches?
Unless you light the switches, consider putting them somewhere you can easily find them in the dark.

All three switches can be on the same 12v supply- the amperage needed to throw a relay is minimal and they won't interfere with each other. Your power going out of each switch needs to be isolated, as well as to and from each relay. The supply for your switches should also come from a 12v ignition source or your headlight switch so when you turn the Jeep off and leave the switches on they don't stay on.


And it's great you're using relays, but don't forget the fuses too!

Last edited by alpine.adrenaline; 04-19-2017 at 04:30 PM.
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Old 04-19-2017, 07:30 PM
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Originally Posted by alpine.adrenaline View Post
You could also run 12v to 30 and 86 and make 85 a switchable ground. Sometimes I use this method for cooling fans etc because if the switch shorts out the device just stays on.
before posting i thought of mentionning this but i wasn't sure what method is best / for what reason(s) . thanks for mentionning
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Old 04-20-2017, 06:47 AM
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Originally Posted by alpine.adrenaline View Post
Unless you light the switches, consider putting them somewhere you can easily find them in the dark.

All three switches can be on the same 12v supply- the amperage needed to throw a relay is minimal and they won't interfere with each other. Your power going out of each switch needs to be isolated, as well as to and from each relay. The supply for your switches should also come from a 12v ignition source or your headlight switch so when you turn the Jeep off and leave the switches on they don't stay on.


And it's great you're using relays, but don't forget the fuses too!
Being able to find them was my thought in putting them on the console. And they would be accessible from either side. I hadnt thought about wiring it to a 12v ignition. Good idea. Fuses are your friend lol
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Old 04-20-2017, 10:29 AM
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I think im gonna use these relays:
Amazon Amazon


And these switches:
Amazon Amazon


And put them on the front face of the center console, to the passenger of the e brake
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Old 04-22-2017, 04:39 AM
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I ran 2 150w lights for a couple minutes without relays once... before the smell of something burning took place . Switch pretty much melted.

I had a after market LED lighted switch on the dash that blinded me, had to put black tape over it. Damn thing would burn a hole in your retina. Didn't notice til nightime when I would actually use the flood lights. Not saying what you picked out will, just a fyi.
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