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Can you connect a relay to the headlight wire?


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tbilyk 
Member - Posts: 1
Member spacespace
Joined: September 01, 2002
Location: United States
Posted: September 01, 2002 at 11:40 PM / IP Logged  

Is there a problem connecting the positive wire from a headlight into a relay?  I am trying to setup my aftermarket driving lights so they come on with the ignition but turn off when the headlights are turned on.

I have a spare socket on my fuse box for the igition on power supply, so that part is not problem.  What I thinking might work was adding a Bosch 30amp relay under the hood.   First thing I added was a diode between pins 85 and 86 (prevent inductive kickback). 

Pin 30 goes to ground.

Pin 85 goes to the positive (hot) wire of the headlight.

Pin 86 goes to ground.

Pin 87 not used.

Pin 87a goes to ground wire leading to the Aux light's relay.

Note: I am using a Painless Aux relay wiring kit.  The kit instructions are to connect the red power from the relay directly to the battery, the black wire from the relay goes to ground.  Blue wire goes to the aux light switch.  The red wire on the switch goes to fused positive and the black wire on the switch goes to ground.  I am keeping this same setup except placing the Bosch relay between the ground wire of the Aux Relay and true ground.

Will this work?  Will it affect the brightness of the headlights,  Is there any problems with using a 12V (up to 20 amp) wire to energize the relay?

HotRod53F100 
Copper - Posts: 84
Copper spacespace
Joined: May 12, 2002
Location: United States
Posted: September 03, 2002 at 7:25 PM / IP Logged  
I'm not familliar with the particulars of you Painless terminal numbers ect but....you absolutely can connect into the headlight circuit. You are trying to drive a relay from that circuit that draws maybe 50 ma, the headlights draws tons more than that. It won't effect your headlight brightness at all. Since your tieing into the light circuit for switching only, the power will come from your aux or bat circuit to light your fog lights, not the headlight circuit. Here in PA, you are required to tie into the low beam circuit to trigger the fog lights and they are to turn off with the high beams.
HotRod
Philo 
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Member spacespace
Joined: August 07, 2002
Location: United States
Posted: September 03, 2002 at 8:48 PM / IP Logged  
You should have no problem tying into the headlight circuit, but I would never put a relay under the hood. The factory relays under the hood are under a cover and sealed from moisture because they are suceptable to problems if they get wet. You should be able to find a low current circuit near the head light switch, or on the column. depending on your vehicle, and do the wiring inside the car. if you post your year make and model, I may be able to help more.
17 years in the 12 volt industry MECP 1st Class
mobiletoys2002 
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Joined: April 12, 2002
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Posted: September 03, 2002 at 8:53 PM / IP Logged  
i agree with philo dont put relays under the hood ever they will fail and it is not worth it. Unless you can keep this relay not wet under the hood than go ahead and put it under the dash using one of the trigger wires off the headlight switch.Can you connect a relay to the headlight wire? - Last Post -- posted image. 
djfearny2 
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Silver spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: September 23, 2002
Location: United States
Posted: September 23, 2002 at 3:48 PM / IP Logged  

i have answered many questions today and the standard starter kill relay setup works for a lot.

here is how it is done.

pin 85 connected to the positve wire of the headlights loacated at headlight harness.

pin86 to constant ground

pin 87a to a possitive 12 volt wire that turns off with ignitons preferable place is to look in fuse panel

there is things to buy that can add a fuse to the panel in seconds. get one works with large and mini fuses

put a ten amp fuse in that.

pin 30 run to possitive wire of driving lights

your done test it turn ignition on and lights should go on . while ignition is on turn on headlamps and driving lights will go off

email me for help djfearny2@aol.com

cpgoose 
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Joined: July 08, 2002
Location: United States
Posted: September 27, 2002 at 10:28 AM / IP Logged  

Can I add on to this question/answer?  I just want my headlights to come on through an AUX channel from my alarm.  Can you explain how to wire a relay to do this?

THANKS!

cpgoose 
Gold - Posts: 1,098
Gold spacespace
Joined: July 08, 2002
Location: United States
Posted: October 02, 2002 at 10:47 AM / IP Logged  

Is this the correct hookup for just controlling the headlights with a AUX channel on the remote?

  • 87  ==  12v+
  • 85  ==  Ground
  • 86  ==  AUX channel
  • 30  ==  Headlight + wire
  • 87a =   Not used
omega 
Copper - Posts: 54
Copper spacespace
Joined: July 04, 2002
Location: Canada
Posted: October 02, 2002 at 11:36 AM / IP Logged  

Hey CP...  Actually you'd probably use +12V on pin 85 as AUX outputs usually output a GROUND pulse.  However unless your AUX output on your alarm has a feature for "latching" that will only turn the headlights on momentarily (for a "pulse").  Some alarms have a feature in which the aux output stays on as long as you hold the button so in that case you'd get them to be on as long as you held the button.

If your alarm does not feature latching (and you want to turn the lights on with one press and off with the 2nd press) you need to get a latching relay and hook it up the same way.  The only thing is that with the latching relay the relay energises and rests in the "on" position on when the button is pressed once.  Energising the coil a 2nd time will "unlatch" or turn "off" the relay thus extinguishing the lights.

Finally if you could get a Time-Delay relay (or use an appropriate capacitor), you could make it so one button press will activate the lights and stay on for a few seconds or minutes and then go off automatically.

mobiletoys2002 
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Joined: April 12, 2002
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Posted: October 02, 2002 at 1:44 PM / IP Logged  
hey cp goose if you are talking about th eviper 550 you can latch this output many different ways oin the aux channel and do many things easier.

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