Hooking relay to headlights to switch foglights. Help please. - TTORA Forum
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post #1 of 7 (permalink) Old 12-06-2007, 06:35 PM Thread Starter
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Hooking relay to headlights to switch foglights. Help please.

Bare with me folks. Im 17 and have some knowledge about wiring relays. Ive search some and havnt found anything about using the headlights as a switch for a relay.

I have a 1995 3.4L tacoma 4x4. I have my fog lights wired through a toggle switch on my dash with an led indicator so I dont forget to shut them off. Im sure I am loosing power through that setup and I dont always see the led light to remind me to shut them off.

What I would like to do is hook a relay up to turn them on. What my plan is is to use the headlight positive wire to switch the relay on then the relay would switch the fog lights on from there. So hopefully the end resault would be when I turn my driving lights on my fogs also turn on.

I was wondering if I needed a Single Pole Double Throw relay or a Single Pole Single Throw relay.

In diagrams I see that one end of the coil is grounded. This poses a problem because if the positive from the headlights are connected to the relay to turn the relay on then it wont be turning the headlights on. I was wondering if I could just use a wire connector and tap off the wire going to the headlights to switch on the relay.

I was wondering If I could use a double throw because I found a good deal on ebay here.

I know some of it is confusing to begin w/ and probabaly even more confusing after I have tried to explain it but I think you guys can figure it out so any helps appreciated. Thanks, Jamie.
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post #2 of 7 (permalink) Old 12-07-2007, 08:38 PM Thread Starter
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Any incite??????
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post #3 of 7 (permalink) Old 12-07-2007, 09:33 PM
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for general aux light wiring use a standard 4-pin, 30a relay with #30 to battery or aux fuse block; 85 to ground; 87 to lights and 86 to the switch.
basic diagrams

fogs are normally wired to be switched on when the low-beams are on (mandatory in some states) so you have to tap into the lo-beam lead wire as the 12v source. driving lights are normally switched with the hi-beams via the same procedure. You can hook things up so they can be switched independently, however, or even together...just gets a little more complicated.

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post #4 of 7 (permalink) Old 12-07-2007, 10:42 PM
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Originally Posted by jpen123 View Post
What I would like to do is hook a relay up to turn them on. What my plan is is to use the headlight positive wire to switch the relay on then the relay would switch the fog lights on from there. So hopefully the end resault would be when I turn my driving lights on my fogs also turn on.
I'd hook them up on a separate switch, you may not always want your fog lights to turn on with your headlights... And if the Tacomas are the same as the previous generation pickups, the lighting switch is actually on the ground side of the headlight circuit. Power goes to your headlights, and the light switch grounds either your high or low beams to complete the circuit.

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post #5 of 7 (permalink) Old 12-07-2007, 11:23 PM
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You could use a single-pole double-throw if that what you get a deal on. You just need to figure out which are the normally open and normally closed connections (use a cheap multimeter, you will want it if you have problems later). You will want to use the normally open terminals.

I would take a wire from your dash or side lights, through your switch, through the relay coil, and to the low side of your headlight low-beams (red-green on a '99). As has been mentioned, these headlights are switched on the low side of the bulbs.
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post #6 of 7 (permalink) Old 12-08-2007, 01:28 AM
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Originally Posted by Rebuilt98 View Post
My 98 isn't that way so I doubt the rest are either. I just did a similar wiring job a few weeks ago. Wired my Hella's to come on with the High beams. Just tap into the switch wire that triggers the high beams below the dash. Pretty simple. I found the wire for the low beams too I think it was green and red or red and green or something, it's in the Hayne's manual.
97's switched the ground
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post #7 of 7 (permalink) Old 12-08-2007, 09:52 PM Thread Starter
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Wow, thanks you guys. You have helped allot. Ive got 5 Single Pole Double Throws on the way that I got on ebay. I think 16 bucks shipped is good for 5 with wiring harnesses for each included.

Thanks for the quick responses.

I think I am going to hook up my relay to power on when the dash lights turn on. Then I will be able to have them on high beams and low beams. To do so can I just tap into the Dash Board Lights wire coming from the small fuse box located under the dash or what do you suggest. I also have a haynes book for my tacoma so if you would like to refer to any pages in that for any further help then I will check it out.

Someone mentioned that I do something just incase I dont want the fog lights on all the time. I was thinking since I already have 2 toggle switches mounted on my dash I will just use one of them.

I also bought some lights to place underneath my truck. I plan to place one on the drivers side frame inner area and point it towards the passengers side and vice-versa for the other. Then use a relay to wire it to my dome light so when I open my drivers side door or passengers side door the lights underneath light up the ground. I would also have a switch hooked to it so I am able to turn on the dome light while in the truck without having the auxilary lights underneath turning on. If this sounds a little pointless or w/e its because It kind of is. Usually around this time of year I get out of my truck and I step in a slush puddle (live in Maine) or the tendancy to drop things and the fact that it gets darker sooner now has me thinking its worth it so we'll see how that goes. Another reason for doing so is I might have some time on my hands so I try and keep busy. If anyone else has some cheap ideas that you think id like feel free to suggest them.

Thanks again you guys.
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