b5rider

I bought 2 pairs of lights for my rack and was wondering if I could wire them to one switch? if so, what is the easiest way to do this? I am trying to minimize the wire runs and simplify the wires under the hood. I will add another pair in a week to the bumper (for a total of 6 lights), and didn't want three switches cluttering the dash and 40 miles of wire to run. Thanks in advance

rickyj

Hard to answer without knowing what the wattage of the lights are, and what the amperage rating of the switch is. If you have 100 watt lights, six of them, that is 600 watts so you would need a switch that had a 600/12=50 amp capacity. Since as far as I know you aren't going to find a switch that works and running the wire to the switch panel would be a serious pain, you should just count on using a relay. That will be easier anyways. Wire some thinner wire from the battery to the interior switch, then back to the relay. The high current wire can go from the battery (to the fuse) to the relay, then you can split the wire from there in a current appropriate gauge to each light. Shouldn't be too bad as long as you use the right sized wire and relay. Just remember add up the total wattage of the lights, then divide by 12 for the amperage of the relay.

www .powerstream.com/Wire_Size.htm

So, if you have 6 100 watt lights, use a 50 or 60 Amp fuse to the relay and 10 or 9 gauge wire, then 20 or 21 gauge wire to each light is fine - but since each wire can't handle that load you might want to pair up the wires on a 20 amp fuse after the relay or 10 amp fuses for each wire after the relay.

Edited to add the answer - yes, there isn't anything preventing you from running all lights on one switch.

JK-Ford

YES. But this means that you will be building your own harness. Or modifying store bought harness. You only need one circuit from your fuse box taped into an "ignition" fuse tap to power your switch ( or switches ). And you will need one relay per each pair of lights feed directly from the battery.

Except for very light loads such as LED's, always use a relay. And, I would not suggest installing any circuits over 30 Amp. Conductors bigger than 10 awg become very hard to work with. Unless you are building a power distribution block.

Distance does have a roll in determining wire size. But, as a general rule of thumb, only after 100 ft. So, unless you are going to run a single conductor around your jeep a couple of times before landing it, length is not a factor here. Just simply use the correct gage conductor to carry the load.

b5rider

Thanks for the info. I am going to link the 4 lights on the rack to one switch and the other two to another switch. I am understanding that I can splice only the switch wires together, but I will run separate wiring and relays to each of the pairs. two more questions:

1 how do I wire the four rack lights to the high-beam switch? can I use the fuse box mod? If so, how do I wire the two circuits together to the single fuse?

2 how do I wire the 2 bumper lights to the fog switch?

OnBelay

Install a relay
Run a wire from your battery to your relay
Tap your high-beam +12V wire and connect it to the relay
Don't forget to properly ground your relay.

This will turn the lights on and off with your brights. The current for the high beams will trigger the relay. You can do the same with the fogs as well. I don't recommend this config, but it is possible. I'm actually in the process of designing the switches and diagram for my future light configuration. I'll be using a DPDT switch so that I can turn them on manually, turn them off completely, or have them turn on when the high beams/fogs/etc. (depending on light) are activated.

OnBelay

First off, go HERE to calculate wire size: hxxp://beta.circuitwizard.bluesea.com/

Why would one bother running 21AWG even if they *could* get away with it? Sheesh, at least run 16! The difference in size isn't really that much ... and these vehicles are subject to various environmental extremes! FYI I run 12AWG for lighting circuits ... and all my switches run 16AWG, regardless. Why not?

As for ampacity, I totally agree. But don't forget that there is another metric to be concerned about: VOLTAGE DROP. Even though a certain AWG wire can handle a specific amount of AMPS, it might not deliver acceptable current to the end point.

JK-Ford

Since you are a novice wireman. I would recomend purchasing a couple of lighting harnesses from your local auto store. They will come with everything you need. And basick instructions to install. Then all you will need to do is to modify the switches to suit your needs. However, I would have to recomend keeping all the switches.

You will need to tap into your fog light circuit to trigger the relay.

IYou do not have to agree with me. It's your jeep. My information comes from my 25 years experience and the National Electrical Code ( NEC ). I did not recomend installing 21 awg conductor. Or Installing anything over 100 feet. All though you could if you were an electriian and knew how to do it.

This can be done safely if you use diodes to block spikes and back feeds. And strategicaly placed fuses to protect the circuits. I used two sets of relays on my system to cut down on the control wireing. One set for auto control. And one set for manual control.

JK-Ford

Sorry. Let me clarify. I am only trying to make the point that there are methods to use diffrent size conducters in different situations. But they have to be used properly. Just like it was stated earlier about voltage drop and ampacity. However, I NEVER recomended to anyone to use a circuit beyond its limits.

Edited:Someone else recomended the 21 awg wire. I recomended the aftermarket harness

rickyj

The original poster should use a higher gauge wire if for no other reason than it is easier to work with. But it isn't going to catch on fire if he uses 20 gauge wire. My original recommendation was probably not the best one but it was late and I was tired. You can always use a higher gauge with no ill effect. But will it work? Sure. I am surprised by a forum that doesn’t give a second thought to pulling federally mandated rollbar padding, drastically changing the forces on the hub bearings with non factory backspacing or wheel spacers, or bumpers that change the impact pulse of a collision is so freaked out about wiring. I am guessing this is a waste of time, but I have so much time right now I might as well waste it.


Using 20 gauge wire the total resistance for a 10 foot section would be 0.1036 Ohms. You can calculate the heat disapated by the wire in Joules with E=(I^2)*R*t. So if you left the lights on for 10 hours straight, that would be about 250 BTU per light. For the whole set of 6 that would only be 1500 BTU, so if you managed to put all of that heat inside of a 5 gallon bucket filled with water that leaked no heat the entire time you would only be able to bring that water from 70 degrees to 105 degrees. For 10 hours of on time. So dusk to dawn. Of course, the wires are going to be losing heat the whole time, so it isn’t going to catch on fire. I believe, if the JK heater is 60,000 btu (probably higher as it is a kick ass heater) it would put out the same amount of heat in 15 minutes, probably 10.

Disclaimer – I am not an electrical engineer, but I did consult my brother who is close to being one and he thought it was OK (as in work but not ideal) as well. But it was quick email, and most of my calculations were self taught in the past 30 minutes or so.
Back to the original question – just use 14 gauge or something.

OnBelay

Yep! As a matter of fact, I created my backup light wiring harness with the diodes and fuses ... per your recommendation. Three-way switch is working awesome. Thanks again.