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Wiring two 50 watt exterior lights

3K views 24 replies 7 participants last post by  M.T.N. 
#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
 
#2 ·
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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#4 · (Edited)
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.
 
#5 ·
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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#6 ·
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.
 
#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.
 
#11 ·
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
 
#13 ·
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
 
#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.
 
#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.
 
#21 ·
Just finished all of the wiring and everything, but the lights aren't turning on. I'm guessing I need to buy a volt meter to test the different parts of my wiring? Not exactly sure why they don't work as of now. Everything is connected well and all.
 
#24 ·
If you are supplying the switch direct from the battery (not through a ignition switched circuit), then yes with the vehicle off throwing the switch will make the relay click.

If you are going through a switch circuit, vehicle does not have to be running, just in the on position.

Check your grounds. First the relay ground off of 85 or 86. Then the light's ground. Sometimes bolting them to the bumper is not enough. You need to run a ground wire back to the battery. Same size as the feed wire. If any of your grounds are by a screw to the body, make sure the paint is cleared away. Electrical connections are bare metal to bare metal.
 
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