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wiring help! is this safe???

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Old 03-20-2011, 05:29 PM   #41
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Note: I'll help, but I'm not responsible for any fire/damage/injury.

If I read your posts right, you have 3 55W bulbs and you want to tie all three together to a single wire that goes to the relay? From the "Basic Circuit Design" section of my writeup, I calculated ~5 amps worst case scenario for each bulb. That means the three bulbs will pull at ~15 A worst case. Therefore, from the wiring section, a conservative wire would be a 12 gauge wire. If you know you can get a high quality wire, maybe you can get away with a 14 gauge. My conservative recommendation would be to use 12 gauge wire with a 15A fuse. This should sufficiently protect the wire. If you blow the fuse too often and know you have a quality automotive wire, you should be able to go to a 20A fuse....or move up to a 10 gauge w/ a 20A fuse.

Again, these are conservative numbers and you should be ok. Again, I'm just trying to get you in the right direction, but I take no responsibility for your decisions.

EDIT: I just realized you're playing with an unsafe condition!!! You always need to size the fuse for the smallest wire in the circuit (e.g. the three individual wires going to the lights). It sounds like you're using 14G wire, so you'll need a fuse no bigger than 15A conservatively!! The other way to do it is provide a big fuse (e.g. 20 or 25 A) for the entire circuit, then provide 3 10A fuses for each light. This ensures each smaller wire is protected. Lastly, the other option which is simpler is to simply run the three lights all the way to the relay, which eliminates the complexity of a bigger wire and fusing.
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Old 03-20-2011, 05:44 PM   #42
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I can't take credit for this diagram but this how I wired my fog lights. I used 10 awg for the pos and neg from the battery and 14 awg for every thing else. it maybe overkill but better then a fire. I also pulled off the plastic insulation from the crimp connectors and soldered and shrink tubed all the connections. Plastic wire loom and zip tyes. wiring help! is this safe???-foglite-wiring.jpg
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Old 03-20-2011, 05:51 PM   #43
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This wiring stuff is confusing! Sounds like I should just upgrade to all 12g wire with 10g going to the batter...were it says switch to battery (THAT'S HOW I HAVE IT NOW) could I just put that wire to a ground instead of to the battery? I need to make a list of the crap I'm going to need now haha
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Old 03-20-2011, 05:53 PM   #44
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So I should re wire the harness from the 3 lights to the relay with 12g...then 10g from the batt to the relay ( with a 25amp fuse) and I can just use my 14g from the switch to the relay
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Old 03-20-2011, 06:00 PM   #45
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If you already have a bunch of 14G wire, that will do just fine for each individual light...but you're right, to be totally safe a 10G wire would do some good for in between the battery and the 3 lights. Just remember you need to fuse for the smaller 14G wires, therefore a 15A fuse should work ok. Again, this is a conservative fuse, so if your 14G wire is quality wire, you can likely get away with a 20A fuse.

Just to put it all in perspective, in my personal build I have 2 55W fog lights used for bed lights. I am using a 15A fuse and 14 gauge wire running from the engine bay back to the bed. The wire is a high quality 90 degree C automotive (e.g. fire/gas/grease resistant) wire.
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Old 03-20-2011, 06:06 PM   #46
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Quote:
Originally Posted by island taco View Post
I can't take credit for this diagram but this how I wired my fog lights. I used 10 awg for the pos and neg from the battery and 14 awg for every thing else. it maybe overkill but better then a fire. I also pulled off the plastic insulation from the crimp connectors and soldered and shrink tubed all the connections. Plastic wire loom and zip tyes. Attachment 93398
I need to clear up a few things.

- 10 awg from battery to pin #30
- 10 awg from ground to pin #86
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Old 03-20-2011, 06:07 PM   #47
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So I would add a 15a fuse between the switch and the raly correct? I already have the lights completely wired up with all 14g and they work great, I'm just scared for fires
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Old 03-20-2011, 06:13 PM   #48
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The fuse goes between the battery and the relay, located as close to the battery as possible. If the switch is directly powered off the battery, then yes you should also but a fuse between the battery and the switch too. But if the switch is tapped off a factory wire (i.e. ignition or cigarette lighter), then the factory fuse should protect the switch and wire just fine (assuming you're using your 14 gauge wire).

Check out the diagram below too. The fuse value isn't right, but it represents what you're trying to do.

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Old 03-20-2011, 06:19 PM   #49
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Yea, my switch is connected to the battery, I also have bed lights to that have no relay, but it does have a fuse, but I think the fuse is in the cab...
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Old 03-20-2011, 06:26 PM   #50
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Based on that diagram are they using 10g or 12g from the battery to terminal 30?
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Old 03-21-2011, 07:34 AM   #52
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If I'm using a relay do I still have to run a wire from the battery to the switch???
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Old 03-21-2011, 09:30 AM   #53
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Quote:
Originally Posted by kinkrider101 View Post
If I'm using a relay do I still have to run a wire from the battery to the switch???





No it is not necessary to run the switch from the battery if using a relay. It will still need 12v if you are wiring like the diagram above.
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Old 03-21-2011, 02:16 PM   #55
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So I can't just run a wir e from the switch to slot 86? The switch still has to have a power wire? Or will the power be provided throught the 86?
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Old 03-21-2011, 05:17 PM   #56
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Quote:
Originally Posted by kinkrider101 View Post
So I can't just run a wir e from the switch to slot 86? The switch still has to have a power wire? Or will the power be provided throught the 86?
I'm not sure understand the inner workings of a relay, take another look at my electrical basics thread (link in sig).

Post 86 of the relay is the control input. Without this input, the relay doesn't know when to turn on, and therefore your lights will never turn on. Post 30 is the high voltage input, post 87 is the high voltage output. Post 86 is the control input and 85 is the control ground.

In this situation, think of a relay as an amplifier. The switch represents the low-level input that doesn't have high voltage capability. Therefore, it is simply used to operate a relay which "amplifies" the signal and carriers the high voltage/current load.

If you want the lights (via the relay) to turn on when you turn something else on (i.e. with the fog lights or headlights), then simply tap the power wire for those lights and run it directly to 86. In this case you don't need another switch because the fog lights on/off act as the relay control input.
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Old 03-21-2011, 06:13 PM   #57
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Thank you for all your help! I un wired all the old wires and bought a relay today, in all the diagrams it show the switch going into the fuse panel, but if I didn't decide to attach a wire from the switch to the fuse box, then it would have to be run to the battery. Then there would be a 10g powerfull wire coming straight into the dash...
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Old 03-21-2011, 07:40 PM   #59
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I'm using all 12g wire now with 10g from the battery and for the grounds. I'm having trouble finding a 25a fuse, I can oly find 20a and 30a... won't it be a pain to run a 10g wire through the firewall? Another question. My bed lights were wired under my truck and then then came up right through the engine bay, so the wires were kinda burnt from the cats being very close, I can't figure out where to run the bed light wires without having to go thought the engine bay?
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Old 03-22-2011, 05:36 PM   #60
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To answer your questions:

1. As stated in post #41, your 3 55W lights will pull a cummulative ~15A worst case...a low efficiency 10 gauge wire can handle 30 amps, so you are perfectly fine there. Each bulb will pull ~5 amps worst case through its 12 gauge wire respectively...a low efficiency 12 gauge wire can handle 20A, so you're okay there too. Next, you need to choose a fuse that will protect the smallest wire in the circuit (e.g. the 12 gauge wire(s)). Since the 12 gauge can handle 20A, you need to protect the wires below this value, so I would suggest a 15A fuse. The possibility of the lights pulling a total of 15A is highly improbable, so it is better to be safe than sorry. If however you blow to fuse often, you should be able to get away with a 20A fuse because the 20A max capability of the 12 gauge wire is a conservative estimate...but moving up in fuse size assumes you are using wire meant for automotive applications and not some indoor type cheap wire.

2. Yes, it will be a pain to run a 10 gauge wire through the firewall...and highly unsafe!! The solution is to mount the relay in the engine bay, which is one of the benefits of using a relay...allow the relay to be contained in the engine by allowing only a smaller low-power wire to go from the switch in the cab to the relay in the engine bay.

3. Bed light wiring: check out my build. There's pics of how to run wires through the firewall, under the carpet, and back underneath the truck via pass-throughs in the floor. I did this for both my running board lights and bed lights.
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