lighting relay
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=109085
Printed Date: June 11, 2024 at 3:10 PM
Topic: lighting relay
Posted By: fish2live
Subject: lighting relay
Date Posted: November 20, 2008 at 12:42 PM
My objective - to have aux Hella Rally lights that will work with an OEM switch on the dash via a relay - this is working great today. I want to add (in red in the diagram) the ability for those same lights to ALSO switch ON when the High Beams are activated. The issue I'm having is that the High Beams are Neg ground and are hot when off, and go cold when I turn them on. I posted a while ago and had the following advice: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
Ground terminal 85 The 12 volt switched wire that controls the relay to terminal 86. Terminal 30 goes to the battery via a fuse mounted at the battery. Terminal 87A will supply voltage to the light. The only problem with this setup is the coil of the relay is energized all of the time. It WILL run a battery down. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I'm a little confused (sorry, I'm a wiring idiot!!).... would the following diagram work? Do I need BOTH diodes (or any diodes at all?) Items in black are installed and working - red is new and open to your suggestions.. 
------------- rookie
Replies:
Posted By: fish2live
Date Posted: November 20, 2008 at 1:27 PM
if you click on the pic the lines will clear up a bit with better resolution... at least that's what happens on my computer...
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rookie
Posted By: fish2live
Date Posted: November 22, 2008 at 9:25 PM
just wondering if nobody understands this or maybe my question just doesn't make sense??? i figured I'd have a response by now.....  ------------- rookie
Posted By: fish2live
Date Posted: November 25, 2008 at 12:36 PM
Did I say something wrong? I'm used to at least SOME type of response on other boards..... to not have a single one is rather strange. ------------- rookie
Posted By: dualsport
Date Posted: November 26, 2008 at 9:15 PM
Sorry I got to the party late, but I just stopped in to browse around a bit- mebbe everyone's prepping for their turkey dinner- 
One thing you could do is to connect an ignition switched line to terminal 85 of your new relay with a diode in series (with the cathode towards the relay). If you connected it to ground the way you show in the diagram, the relay would always be on until you turn your high beams on, not what you want.
Connecting it to a switched ignition line, the relay only energizes when your ignition is on and the high beams switched on. When the ignition is off (and I assume you won't want to turn on your driving lights then), the diode will block any current from backflowing from your high beams.
The rest of the circuit you could use as you drew up (you may want to add a diode between your OEM switch and the relay terminal 86 if your car doesn't like any backfeed from the other relay.) If it doesn't care, you can wire it in directly as you show in your diagram.
Or you could use your added relay to power the aux lights directly, though that means you'll need heavy duty wiring instead of just some thin control wires. I'd just use the relay to control the first one like you did, that'd be the best way.
Posted By: fish2live
Date Posted: December 03, 2008 at 1:55 AM
Hi there dualsport (by the way, I have a KTM EXC400 that I Dualsport!!) - anyway - THANK YOU VERY MUCH for the response - I don't think I quite get what to do for your first suggestion. The line going into 85 on the new relay is a ground line, but you're saying make it a 12v positive power line that is only switched on with the ignition..? Right? I think I get that part, but wouldn't that mean that the relay has 2 power lines in - one at 85 and one at 86 - both energized when the ignition is on? Sorry again - I am a wiring idiot!!
-------------
rookie
Posted By: dualsport
Date Posted: December 03, 2008 at 1:07 PM
If I read your description correctly, your high beam line (the one you were going to use to control the relay) is normally sitting at 12V when the high beams are off, and goes to ground when you turn on the high beams.
If that's correct, my suggestion was to use that as the ground side of the relay coil, so that the relay is only turned on when you have the high beams on (so the line is grounded), and the ignition is on.
The 12V for the relay is coming from the switched ignition line, and the ground is from your high beam line. You'll have to flip the direction of the diode that you show in the diagram so that the current flows out of the relay coil towards the high beam control line, if you hook it up on the high beam side.
Maybe I should point out that a relay works when there's a difference in voltage between the relay coil input terminals. If you apply 12V to both sides of the coil, the net voltage is zero, same as if both sides had zero volts on them. Zero volts means the relay is not turned on.
In your case, the relay will only see 12V when you turn on the high beams, which brings that side to ground, while the ign switched 12V is supplying the power.
If your ignition is off, and you have the high beams off, then that would put 12V across the coil in the reverse direction, which would also turn it on, which you don't want happening. So that's why you would have to add a diode, to block the current flowing in that direction.
KLR650 :-)
Posted By: fish2live
Date Posted: December 13, 2008 at 11:41 AM
alright - it worked perfect!! THANK YOU!!! I have another question soon as well, stay tuned ------------- rookie
Posted By: dualsport
Date Posted: December 14, 2008 at 8:17 AM
Good to hear it worked out- nice KTM!
Posted By: fish2live
Date Posted: December 14, 2008 at 3:09 PM
Thanks, it's a 453 actually (big bore kit) with a Yoshi pipe and Rekluse auto-clutch. I'll post my other question in another thread!! ------------- rookie
Posted By: jackal342
Date Posted: May 29, 2009 at 3:21 PM
Ok, so I'm kind of lost. I have a 4 prong relay (it has 86,87,85,and 30/51 on the diagram on the back) I want to have my car run the low beams normally, but when the high beams are turned on I want the low beams to come on with them too. (Right now when you turn on the high beams the low beams turn off). How should I wire this? A friend told me to put the high beams on 86 (switched) the lows on 30/51 (load) the ground is 85 and the constant is 87. Do I need to run a constant for the lights? I'm so confused.... Any help would be great. Thanks guys.
Posted By: i am an idiot
Date Posted: May 29, 2009 at 7:04 PM
You can not do it with the relay you have, you need a Single Pole Double Throw relay, you have a Single Pole Single Throw device. You need to cut the wire that now feeds your low beam lamp. Connect the vehicle end of that wire to terminal 87A of the relay. Connect the lamp to terminal 30. Terminal 87 needs to be connected to the battery. 
Posted By: jackal342
Date Posted: May 29, 2009 at 10:39 PM
Thanks a lot! I'll go get the new ones tomorrow! You have helped me so much! Thanks again!
Posted By: dualsport
Date Posted: May 30, 2009 at 2:41 AM
Was there a problem wiring it as described by your friend using the high beam to control the relay and switching the constant power to the low beam? You'd only be tapping into the low beam in parallel with its original power rather than opening up the connection.
It would then apply power to the low beam through your added relay when the high beams are on, but do nothing when the high beams are off.
You'd need the SPDT only if you need to maintain isolation from the low beam power feed for some other reason.
Posted By: jackal342
Date Posted: May 30, 2009 at 11:26 AM
I didn't wire it up at all because I wasn't too sure if he had it right. But thats how I want them to run. I just want them to run normal when in low beam mode, but when the high beams are on I wanted the lows to come on too. See what I did was I had a 1997 firebird that used a single headlight for both high and low beams so when you went from low to high the lows would turn off and the highs would turn on. But I changed out the front end of the firebird to the 98-02 front. That front end has two lights one high and one low. The true 98-02s have it so when you turn on the high beams the lows stay on too. Someone told me to replace my headlight control module and that would change it, but that didn't work at all lol. It just made it do the exact same thing. So next I moved on to the idea of adding a relay and my friend picked this one up for me. But I just wanted to confirm that he had it right before doing it. Thanks a lot!
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