Basic wiring question

Basic wiring question

Kolea Hara
Kolea Hara

October 18th, 2011, 4:31 am #1

Hey,

I wanted to make my Honda Civic headlights turn off when the engine is turned off. I cut the ground wire for the headlights, added some 18g speaker wire for length extension, and ran them to a relay, which has the switch leads connected to the lighter wires. The lighter only gets power during ACC and ON, so the relay is only powered at those time, which means in OFF the relay is off and the headlights turn off.

The circuit works just fine (with the exception of something burning out that I don't think I'm worried about). The problem is the 18g wire that I used for extensions (I think) was smoking after I'd been driving for about an hour. I touched it and the wire was pretty hot. So I turned off the headlights (since it was still day time. The point of the circuit was that I could just leave my headlights in the 'on' position all the time and not have to worry about turning them off or running the battery down.)

This is the wire that I used (not rated for in-wall use):
http://www.radioshack.com/product/index ... Id=2036271#

I was thinking of replacing it with this (rated for in-wall use, also type C12 (although I don't know what that means)):
http://www.radioshack.com/product/index ... Id=2062648


Does this second wire seem like a better option? IE is it going to not smoke anymore? Or should I maybe bump up the size of the wire? The 18g seemed like the closest match to the stock ground wire that I cut into.
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MildBill
MildBill

October 18th, 2011, 5:09 am #2

You should be using either 16 or even 14 gauge wire for this. The wire you are using is getting hot because of the amount of current it is carrying, only a larger (I.E. lower gauge) wire will carry the current without getting hot.

MildBill
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J. Cook
J. Cook

October 18th, 2011, 5:21 am #3

Hey,

I wanted to make my Honda Civic headlights turn off when the engine is turned off. I cut the ground wire for the headlights, added some 18g speaker wire for length extension, and ran them to a relay, which has the switch leads connected to the lighter wires. The lighter only gets power during ACC and ON, so the relay is only powered at those time, which means in OFF the relay is off and the headlights turn off.

The circuit works just fine (with the exception of something burning out that I don't think I'm worried about). The problem is the 18g wire that I used for extensions (I think) was smoking after I'd been driving for about an hour. I touched it and the wire was pretty hot. So I turned off the headlights (since it was still day time. The point of the circuit was that I could just leave my headlights in the 'on' position all the time and not have to worry about turning them off or running the battery down.)

This is the wire that I used (not rated for in-wall use):
http://www.radioshack.com/product/index ... Id=2036271#

I was thinking of replacing it with this (rated for in-wall use, also type C12 (although I don't know what that means)):
http://www.radioshack.com/product/index ... Id=2062648


Does this second wire seem like a better option? IE is it going to not smoke anymore? Or should I maybe bump up the size of the wire? The 18g seemed like the closest match to the stock ground wire that I cut into.
1) I would put the relay switching on the power side, not the ground side- You'll still need to make sure the relay and line are rated to pass the amperage through it (check the fuse box for the headlight circuit- that's your max rating at 12 volts)
2) I'd bump up the gauge- if the wire is hot, it means it's at or over it's amperage rating. You really don't want it melting and/or sparking a car-b-que.
3) I would not use speaker cable for wiring car headlights, in my humble opinion; there's better stuff made and sold by auto supply houses that will be a better fit for what you are trying to do.
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J. Cook
J. Cook

October 18th, 2011, 5:25 am #4

14 gauge wire is rated, according to my copy of Ugly's, for 20A. Methinks you'll be wanting 12 gauge wire. I'm not sure how much current the civic pulls for it's headlamps, but if it's anything like my last car, it's between 19 and 25 amps, depending on high beam/low beam use.
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MildBill
MildBill

October 18th, 2011, 6:43 am #5

Even though the headlights draw high current (Amps), he should be doing his wiring before the headlight relay, not directly in the headlight side of the circuit. Pretty much all vehicles already have a headlight relay due to current issues, and it is in the control side that he wants to work.

Indeed, if I were him, I would repair whatever he has done already, and go to the headlight switch, and interrupt the power there for what he's doing. I would also add a simple switch that could be mounted close by to 'short' the break in the power lead, so that he can bypass his relay fix should the need arise, such as having the dome lights (assuming they are on the same power lead to the switch) on, for leaving parking lights on when parking in an unusual place at night, etc.

The headlight switch, in most cases, operates the headlight relay, which operates the headlights. The (built-in) relay would draw much less current that the headlights themselves, but he should still match the wire size used in whatever wire he breaks to run thru the relay contacts. In most cases, this will be either 16 or 14 gauge wire.
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Doc Nickel
Doc Nickel

October 18th, 2011, 7:24 am #6

Hey,

I wanted to make my Honda Civic headlights turn off when the engine is turned off. I cut the ground wire for the headlights, added some 18g speaker wire for length extension, and ran them to a relay, which has the switch leads connected to the lighter wires. The lighter only gets power during ACC and ON, so the relay is only powered at those time, which means in OFF the relay is off and the headlights turn off.

The circuit works just fine (with the exception of something burning out that I don't think I'm worried about). The problem is the 18g wire that I used for extensions (I think) was smoking after I'd been driving for about an hour. I touched it and the wire was pretty hot. So I turned off the headlights (since it was still day time. The point of the circuit was that I could just leave my headlights in the 'on' position all the time and not have to worry about turning them off or running the battery down.)

This is the wire that I used (not rated for in-wall use):
http://www.radioshack.com/product/index ... Id=2036271#

I was thinking of replacing it with this (rated for in-wall use, also type C12 (although I don't know what that means)):
http://www.radioshack.com/product/index ... Id=2062648


Does this second wire seem like a better option? IE is it going to not smoke anymore? Or should I maybe bump up the size of the wire? The 18g seemed like the closest match to the stock ground wire that I cut into.
It sounds a lot like you found- or created- a single ground wire, which services both headlights. One headlight should be a minimum of 12 ga; you've got a wire about 50% undersized for just one bulb, let alone two.

As noted by others, you should wire the relays on the power side, not the ground side.

I'm doing this myself at the moment, too. I scored a set of Hella 100W headlight-replacement lights off eBay for $40, which will be going in the Faux-4-2, along with a standard replacement-style halogen high/low light (4-bulb setup.)

I use three relays: One runs the low beams; whenever the headlights are on, both low beam filaments are on, always. Another runs the high-beam filaments of the hi-lo headlights, and the third will run the 100W Hellas.

In a normal headlight system, when you switch to high beams, it switches from the low beam element to the high beam. My setup adds the high beam filaments.

So instead of four filaments (two 55w and two 60w) I'll have six filaments (two 55w, two 60w, and two 100w.)

The hi-low bulb is glass, a halogen "sealed beam", and can take the extra heat. All the wiring will be 12 ga, with all the connections soldered and glue-filled heat-shrunk. The relays will be fed directly off the alternator by a 10ga cable. That's basically how I did it in both the Corvair and the Toronado, and it works great.

Doc.
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sniper1rfa
sniper1rfa

October 18th, 2011, 10:43 am #7

My subaru leaves the low beams on and adds in high beams. I've seen a few other cars that do the same.
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MNSparky
MNSparky

October 18th, 2011, 12:14 pm #8

It sounds a lot like you found- or created- a single ground wire, which services both headlights. One headlight should be a minimum of 12 ga; you've got a wire about 50% undersized for just one bulb, let alone two.

As noted by others, you should wire the relays on the power side, not the ground side.

I'm doing this myself at the moment, too. I scored a set of Hella 100W headlight-replacement lights off eBay for $40, which will be going in the Faux-4-2, along with a standard replacement-style halogen high/low light (4-bulb setup.)

I use three relays: One runs the low beams; whenever the headlights are on, both low beam filaments are on, always. Another runs the high-beam filaments of the hi-lo headlights, and the third will run the 100W Hellas.

In a normal headlight system, when you switch to high beams, it switches from the low beam element to the high beam. My setup adds the high beam filaments.

So instead of four filaments (two 55w and two 60w) I'll have six filaments (two 55w, two 60w, and two 100w.)

The hi-low bulb is glass, a halogen "sealed beam", and can take the extra heat. All the wiring will be 12 ga, with all the connections soldered and glue-filled heat-shrunk. The relays will be fed directly off the alternator by a 10ga cable. That's basically how I did it in both the Corvair and the Toronado, and it works great.

Doc.
Protect your work!
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Kolea
Kolea

October 18th, 2011, 1:45 pm #9

Hey,

I wanted to make my Honda Civic headlights turn off when the engine is turned off. I cut the ground wire for the headlights, added some 18g speaker wire for length extension, and ran them to a relay, which has the switch leads connected to the lighter wires. The lighter only gets power during ACC and ON, so the relay is only powered at those time, which means in OFF the relay is off and the headlights turn off.

The circuit works just fine (with the exception of something burning out that I don't think I'm worried about). The problem is the 18g wire that I used for extensions (I think) was smoking after I'd been driving for about an hour. I touched it and the wire was pretty hot. So I turned off the headlights (since it was still day time. The point of the circuit was that I could just leave my headlights in the 'on' position all the time and not have to worry about turning them off or running the battery down.)

This is the wire that I used (not rated for in-wall use):
http://www.radioshack.com/product/index ... Id=2036271#

I was thinking of replacing it with this (rated for in-wall use, also type C12 (although I don't know what that means)):
http://www.radioshack.com/product/index ... Id=2062648


Does this second wire seem like a better option? IE is it going to not smoke anymore? Or should I maybe bump up the size of the wire? The 18g seemed like the closest match to the stock ground wire that I cut into.
Thanks for the responses so far.

Here's the diagram with what I did added in (although the relay switching ground is attached to the cig. lighter ground):


I'm thinking that maybe I should cut the BLU/RED wire leading to the combination-light-switch switch, and put the relay there, since that wire will probably see a lot less power going through it since its just controlling the headlight relays and not the entire circuit.

This will get me away from the wire thats grounding EVERYTHING in the circuit.

Thoughts?
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Kolea
Kolea

October 18th, 2011, 1:57 pm #10

"/"

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The high beams are 60W ea and the low beams are 55W ea, so (60W x 2)/ 12V = 10A is what I would think I'd be seeing through that wire that I've currently got in there.

The blu/red wire leading down into the combination-light-switch is the one I'm thinking I should wire into the relay now, and just get rid of the relay at the ground.

Thoughts?
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