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Discussion Starter · #1 ·
Been looking at tons of different wiring diagrams, but I'm not sure which one is correct. A lot of them contradict each other and aren't the same what so ever. I have a relay that I want to use, but can anyone give me a definite diagram that they know for sure works? Also, what gauges of wires do I need to use for each line?

On a more practical note, how should I join wires? I know the best way is to use a soldering iron, but is it common to just use the twist method and electrical tape for this?

Thanks for your help in advance
 

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This is a good diagram for the wiring. A relay has a coil which is the 85/86 terminals. This is the low current connection which will come from your switch. Connect one side of the coil to negative (85) and connect the other side to your switch. Terminal 30 comes from your battery and should have a fuse as close to the batter as possible. Terminal 87 goes from the relay to your lights and provides the 12+ to them. The other wire on your lights goes to negative. I would personally connect the two positives leads together with a non-insulated butt splice. Both positives on one side with a lead wire back to the relay on the other side. Cover the connection with glue filled heat shrink to seal and protect the connection. You can do the same thing with the negative lead or you can just take each one to a close ground point on the frame.

The terminals on a relay are an industry standard but you can interchange 85/86 as long as one is negative and one is positive it doesn't matter. You can do the same with 30/87 terminals but you run into issues of you have a relay with normally open and normally closed contacts so I would suggest sticking with the standard.
 

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Because of the environments we drive our Jeeps in, bare copper wires quickly corrode. Corrosion will increase resistance and dim your lights. The resistance will cause heating which could cause a fire. In my opinion it is best to solder all connections and use heat shrink tubing. If you can't solder the joints, tin the bare wire ends with solder and use weatherproof crimp connectors.

Here's a diagram for you:


Wire sizes were determined using this chart. 15 foot lengths were assumed.

Wattage = Voltage * Amperage, thus 50 watts = 12 volts * 4.2 amps. Round up to 5 amps as a margin for error. Per the chart, 16 gauge is good for 5 amps for 15 feet at 12 volts.

Double the 5 amps for two lights, so the main fuse would be a minimum of 10 amps. I specified 15 amps for the main fuse just in case instantaneous current was slightly higher when turning the lamps on. Because both lamps run through the relay, 12 gauge wire is required until the two circuits split.

You want to keep the wire from the voltage source to the fuse as short as possible so that the bulk of the circuit is protected by the fuse.
 

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Here is a little simpler drawing. You can use 18 gauge from the switch to the relay, and I would use 16 gauge from battery to relay and from relay to lights with a 15 amp fuse.

This diagram is based on two 100 watt lights so the fuse/wire size will be different on yours.

You should solder and heat shrink or tape your connections.
 

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There is a lot of documentation on reasons not to solder for automotive applications where there is a lot of vibrations. Making a good connection is very important but a proper crimp, using the proper tool, and and a good quality glue lined heat shrink to seal it will make a great connection without causing a joint that could possibly be fatigued due to vibration. Most automotive connections from the factory are crimped and not soldered and most electrical connections made for submerged well pumps are a crimped connections with high quality heat shrink and they are in the water for their whole life span.
 

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There is a lot of documentation on reasons not to solder for automotive applications where there is a lot of vibrations. Making a good connection is very important but a proper crimp, using the proper tool, and and a good quality glue lined heat shrink to seal it will make a great connection without causing a joint that could possibly be fatigued due to vibration. Most automotive connections from the factory are crimped and not soldered and most electrical connections made for submerged well pumps are a crimped connections with high quality heat shrink and they are in the water for their whole life span.
If you have that much vibration in your Jeep, you should find out what's causing it......:D
 

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Discussion Starter · #8 ·
Thanks for everyone's help so far. I want to do this right the first time around and am in no hurry to get it on the wrong way, so I appreciate the debate. Old Dude, I think I'm going to go with your diagram for all the gauges and fuse ratings. Where should the 5 amp fuse go? Closer to the switch or the relay? Also, I bought what seems to be an OEM switch for a 2004 TJ that fits into the dash under the dials if that makes any difference.
 

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If you have that much vibration in your Jeep, you should find out what's causing it......:D
Grab a vibration meter app for your phone and head down the highway. Doesn't feel like a lot of vibration to a person but there is a fair amount that is picket up with the sensors. A lot more if you are doing any wheeling I would guess.
 

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A good/ properly done solder joint on 2 wires in a automobile has yet to ever fail me so I'll not put to much worry in your vibration theory

Not saying it is the only way that works but I am saying it has always reliably worked for me from the 1960s to today so see no reason to change

Now crappy crimp on connections see hundreds of those fail

But if another route works for you great
 

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Thanks for everyone's help so far. I want to do this right the first time around and am in no hurry to get it on the wrong way, so I appreciate the debate. Old Dude, I think I'm going to go with your diagram for all the gauges and fuse ratings. Where should the 5 amp fuse go? Closer to the switch or the relay? Also, I bought what seems to be an OEM switch for a 2004 TJ that fits into the dash under the dials if that makes any difference.
I would put the 5 amp fuse as close to your power source as possible. That way the run to the switch would be protected.

Wish I could help you with using the factory switch; I don't know the pinout on it.
 

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a good/ properly done solder joint on 2 wires in a automobile has yet to ever fail me so i'll not put to much worry in your vibration theory

not saying it is the only way that works but i am saying it has always reliably worked for me from the 1960s to today so see no reason to change

now crappy crimp on connections see hundreds of those fail

but if another route works for you great
x2
 

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Discussion Starter · #14 ·
Probably going to go with soldering if that's what people normally do. For the fuses, do I need to secure them onto anything or can I just let them be? Thanks again for everyone's help. I definitely would have done an amateur job with you guys.

On a side note, I do take my car off road and into mud often so conditions are far from those that regular cars experience.
 

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Probably going to go with soldering if that's what people normally do. For the fuses, do I need to secure them onto anything or can I just let them be? Thanks again for everyone's help. I definitely would have done an amateur job with you guys.

On a side note, I do take my car off road and into mud often so conditions are far from those that regular cars experience.
I'd use a weather-proof fuse holder with a rubber snap-over cover. Auto part stores carry them in their wiring section.

Fuse should be fine if it's zip-tied up away from any moving/hot parts.
 

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Discussion Starter · #16 ·
Sounds good to me. Last question, the wiring attached to the lights seem to be aluminum. Is it okay to splice with copper wire? Or even use copper and aluminum in the same circuit? I don't think I can replace the aluminum wire unfortunately; I don't think I can get into the back of the light housing.
 

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Sounds good to me. Last question, the wiring attached to the lights seem to be aluminum. Is it okay to splice with copper wire? Or even use copper and aluminum in the same circuit? I don't think I can replace the aluminum wire unfortunately; I don't think I can get into the back of the light housing.
Often wires in pre-made harness are pre-tinned. You can take a file to the wires and the plating will flake off exposing the copper if this is the case. I've run into this on the wires attached to fuse holders, relay plugs, etc and they all soldered up and worked fine.
 

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Discussion Starter · #18 ·
Sounds good, I'll give it all a shot this Saturday. Thanks everyone, I'll let you know how it goes.
 

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Discussion Starter · #19 ·
For the diagram, can I hook up the "ignition switched 12VDC power" that is coming from the switch to the positive terminal of the battery?
 
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