switching drls
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=131743
Printed Date: May 16, 2025 at 12:44 AM
Topic: switching drls
Posted By: faja
Subject: switching drls
Date Posted: July 03, 2012 at 8:56 PM
First off, a little background on my car. Canadian Nissan Sentra 2009 using H13 bulbs high and low in one so it has Daytime Running Lights. I installed a projector retrofit and it all works fine but the DRLs are running off the HID high beam and I think that it is way too bright for daytime driving as it is running at full power and not at a reduced rate as when it had the stock halogen bulbs. I also have fog lights that operate via a switch I installed in the cabin so I decided to redirect my DRLs to the foglights. I located the DRL relay and ran the power wire directly to the fogs' lead wire and they work exactly how they should - come on when the car is on, parking brake down and turn off automatically when I turn my headlights on.
The problem I have is that when the headlights are on, if I turn on the fogs via the switch it blows the fuse on the foglight's relay wiring harness. I did some searches and seen some ideas about adding an additional relay and/or using a diode to run power in one direction but don't really have a full understanding of it.
Can someone explain (in layman's terms) how I can wire up the switch to turn the fogs on/off anytime I want to and also have them operate are DRLs at the same time without blowing up something?
thanks in advance.
Replies:
Posted By: howie ll
Date Posted: July 04, 2012 at 2:27 AM
Why not wire the DRLs through an ignition circuit, or even latched via a latching relay from the starter wire?
Then nothing else is affected and you are fulfilling all legal obligations.
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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: howie ll
Date Posted: July 04, 2012 at 2:28 AM
I also have no intention of showing you how to run the fogs at any time, it's illegal in many countries unless you can tell me other wise.
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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: howie ll
Date Posted: July 04, 2012 at 2:48 AM
And here's how to run the fogs properly and legally:-
fogs.bmp------------- Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: faja
Date Posted: July 04, 2012 at 9:18 AM
howie ll wrote:
And here's how to run the fogs properly and legally:-
fogs.bmp
Thank you Howie. I think I'm beginning to understand the effects of the diodes by looking at the diagram.
As for the legality, I am aware of that and I'm not of those people who drive 24/7 with their fogs on, I just want to have the ability to turn them on/off when I choose.
Appreciate your responses.
Posted By: howie ll
Date Posted: July 04, 2012 at 9:32 AM
OK, I screwed that picture up!!
Should have been fog x 2 not DRL x 2.
If you want them on all the time, just feed the switch from the constant that goes to 87 rather than from the headlight feed.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: faja
Date Posted: July 04, 2012 at 12:33 PM
I didn't notice any error because to me the DRLs and the fogs are the same thing.
Maybe you misunderstood my intention of the fogs. I don't want them on "all the time", I want them to act as DRLs which I have done; but when I try to use the manual switch to turn them on let's say at night with my headlights on , it's blew the fuse on the foglight relay harness so obviously I've done something wrong. It only happened the one time but I stopped at that point for fear of risking something more sensitive or expensive like frying my BCM. I need a wiring diagram that would isolate the DRLs and the fogs even tho they are the same thing with different functions. I currently have the foglights set up so they act just as factory DRLs (see post 1) and if I don't ever use the manual switch then they work great - they turn on and off according to specifications. The power to the fogs come from 2 different sources so ideally if I turn on one, it should automatically disable the other
Posted By: howie ll
Date Posted: July 04, 2012 at 12:54 PM
OK, modded, try this:- 7AE_fogs.bmp
Note this is only to power the fogs, DRLs are not affected and it won't blow a fuse, note 5 pin NOT 4 pin relay.
This will give you fogs automatically with low beam headlights or on/off separately.
To turn them off, you will need a a separate switch on the line to 87a or a SPCO switch see this:- fog_switch.bmp
Centre off latched, I'll try and find you an Omron part number, you can order through /mouser or Farnell.
I've now modded the original diagram for it:- 4B9_fogs.bmp------------- Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: faja
Date Posted: July 04, 2012 at 3:31 PM
OK and just to be clear - my DRL power wire is currently hooked up to the "green" wire in your diagram so this will NOT be an issue with power looping back to the DRL relay when the fog lights are on via switch or headlights? If it is, where should I hook up the DRL power wire?
Posted By: faja
Date Posted: July 04, 2012 at 4:10 PM
Hello again Howie,
was browsing the posts and came across this one that you also subscribed to. Since I already have A) a working switch, relay and foglights B) working DRLS with said foglights (just not A + B together), would this setup not work for me if you were to substitute IGN for "DRL power" and add the 2 diodes as depicted? won't the 2 circuits be then isolated so there is no feedback to the DRL module if I turned the switch on.
https://www.the12volt.com/installbay/uploads/2_source_relay.bmp
Posted By: howie ll
Date Posted: July 04, 2012 at 4:25 PM
Either, the LEGAL point you're missing is that the DRLs should come on automatically with the ignition.
Therefore wire the DRLs independently from the fogs without a switch, up to you about the switch, if so use that other diagram with another relay, independently fused.
There's plenty of ways to skin a cat! I'm just trying to keep you legal.
In the UK, DRLs constantly on with ignition, fog lights only with low beam headlights.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: faja
Date Posted: July 04, 2012 at 6:01 PM
Yes, I understand all the above, but my DRLs do come on with ignition and function properly as if they were stock. Not sure if you missed the part where I wired the power lead of the DRL relay to the fogs and they work great, come on upon start and ebrake down, shut off when engine off, shut down when headlights are turned on etc etc. --- there is no switch, the DRL relay is all factory built-in. So what you're saying is leave this as is and then wired up the fog lights like in your previous diagram - is that correct?
Posted By: howie ll
Date Posted: July 04, 2012 at 6:06 PM
Exactly! My last one with the SPCO switch gives you the option of auto switch on with headlights/off/switch on at any time.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: faja
Date Posted: July 04, 2012 at 6:17 PM
howie ll wrote:
Exactly! My last one with the SPCO switch gives you the option of auto switch on with headlights/off/switch on at any time.
OK >> thank you very much, I will give that a try and see how it goes
Cheers
Posted By: faja
Date Posted: July 14, 2012 at 3:14 PM
OK Howie, I have combined some of your ideas along with another poster aka "user error" whose diagram I used to come up with this. Just wanted to run it by you and see if you think this is a safe and viable solution.
Posted By: howie ll
Date Posted: July 14, 2012 at 3:29 PM
Yes, it will work fine.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 23, 2012 at 12:10 AM
hello! this is my first post and i am totally a noob with electronics, i hope you would bear with me -
i would like to use my cheap led headlights as DRLs. i already wired a LED strip by tap-a-fuse from the a power window line under the hood. my problem is how to use a 5-pin relay to make my park lights turn my DRLs off i.e., will this work -
IGN to 30, 87a (NC) to accessory (DRL LED headlights)
Tap from park lights to 85, 86 to ground
87 (NO) not used.
if so, could you kindly provide me with a diagram complete with diodes and fuses? also with diodes, where do i solder them - between the wires of 85 and 86 or the relay's plugs? appreciate greatly your help. thanks!
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Noob Forever ....
Posted By: howie ll
Date Posted: August 23, 2012 at 2:21 AM
It's this simple:- F5D_lights.bmp
Easiest place to wire the relay would be under the hood but please make sure the terminals point down and the relay is protected from heat and damp.
In a cool place in a plastic sealed box (Radio Shack etc.) but remember plastic doesn't withstand heat very well. ------------- Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 23, 2012 at 2:49 AM
howie ll wrote:
It's this simple:-F5D_lights.bmp
Easiest place to wire the relay would be under the hood but please make sure the terminals point down and the relay is protected from heat and damp.
In a cool place in a plastic sealed box (Radio Shack etc.) but remember plastic doesn't withstand heat very well.
thank you !!! :) been waiting for that confirmation though if you don't mind, could 30 and 87a interchanged? also, i read somewhere that its possible to interrupt turning on the DRLs while the handbrake is engaged? how could i do that? thank you for the tip on the placement of the relay in the engine bay, i have this come with the relay and with tape will it suffice to protect the plugs?
 ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 23, 2012 at 3:04 AM
Yes,30 and 87a are interchangeable in this application.
A damp inhibitor spray or lithium grease in a spray work well.
You will need another relay from the handbrake switch wire, I'll post the diagram soon.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: howie ll
Date Posted: August 23, 2012 at 3:51 AM
Here's the same diagram with added handbrake interlock:-
36C_lights.bmp------------- Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 23, 2012 at 3:55 AM
howie ll wrote:
Here's the same diagram with added handbrake interlock:-
36C_lights.bmp
that's great! i have another relay hanging around somewhere and would be useful for the handbrake. thanks much again. now i have to get some h1 harness so as not to destroy the oem in the car. i think i have a 15 amp fuse coming from the ignition, do i need another inline coming from the park light and what rating should it be? ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 23, 2012 at 4:41 AM
No, only the diode. That relay only draws about 1 amp, shouldn't affect the load on the lighting fuse.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 23, 2012 at 5:11 AM
howie ll wrote:
No, only the diode. That relay only draws about 1 amp, shouldn't affect the load on the lighting fuse.
again, i cannot thank you enough. will be working on this as soon as i get my harness :) ------------- Noob Forever ....
Posted By: aponizuma
Date Posted: August 26, 2012 at 7:12 PM
howie ll wrote:
Here's the same diagram with added handbrake interlock:-
36C_lights.bmp
sorry sir to come back with a noob question again - i just want to clarify that should i be looking to tap from the negative of the handbrake warning light in the gauge cluster harness? ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 27, 2012 at 1:42 AM
Yes it's switched NEG, alternatively the wire from the handbrake.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 27, 2012 at 4:29 AM
howie ll wrote:
Yes it's switched NEG, alternatively the wire from the handbrake.
thank you sir for that clarification, i already looked at my car's diagram and its a GREEN/ red cable. but before i do any complicated wiring, i just finished the basic one and i ran into something odd - the drl works when i turn on my park lights instead of vice-versa. is there too much power from the lights? not enough power from IGN? are the relays (i already tried two of them with the same result) damaged? i also put a diode but 1N4148 'cause i cannot find the one on your diagram i.e., 1N4004 - is that the problem? please help. sorry again for bothering you. ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 27, 2012 at 4:32 AM
4148 isn't suitable but check the relay wiring.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: howie ll
Date Posted: August 27, 2012 at 4:35 AM
I just checked that diagram again, it's confusing!
Square on left, "+DRLs" is going from the power source for the DRLs, switch etc.
Bottom right feeds them.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 27, 2012 at 4:36 AM
howie ll wrote:
4148 isn't suitable but check the relay wiring.
wiring sir is as per diagram, i even tried reversing 86 and 85, and putting 87a to 87, and 30 to 87a. could you kindly please explain how would the diode affect how the relay should work for my added knowledge? thank you sir, i will try more to look for 4004 tomorrow. ------------- Noob Forever ....
Posted By: aponizuma
Date Posted: August 27, 2012 at 4:40 AM
howie ll wrote:
I just checked that diagram again, it's confusing!
Square on left, "+DRLs" is going from the power source for the DRLs, switch etc.
Bottom right feeds them.
from your diagram F5D_lights sir, that is all i have done at this time and yes sir +DRL is the one tapped to IGN (my power window fuse under hood). is there are required rating there, i used tap-a-fuse and i think i have 15 amps installed. ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 27, 2012 at 4:42 AM
I've revised the diagram to avoid confusion, now 3 x 1N4004 to hopefully cure any problems. 821_lights.bmp------------- Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 27, 2012 at 5:03 AM
howie ll wrote:
I've revised the diagram to avoid confusion, now 3 x 1N4004 to hopefully cure any problems.821_lights.bmp
thank you sir for bothering to make a new diagram, is it possible to get the one without the handbrake too? ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 27, 2012 at 6:37 AM
ZA7_lights.bmp------------- Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 27, 2012 at 2:06 PM
howie ll wrote:
ZA7_lights.bmp
may i ask sir how do i do the diode between 85 and 86? between the wires or should i solder it between the terminals? ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 27, 2012 at 2:25 PM
Solder.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 28, 2012 at 12:34 AM
howie ll wrote:
Solder.
sir its getting really frustrating. i followed the new diagram with two diodes (i could only find 4006 at this time but the seller said they are all the same from 4001?) and still the drl bulbs goes on with the park lights. i did not solder the diodes yet since i could not make this work yet, there is continuity though so i thought that's just fine at the moment? i tried a test where only drl (30) and ign (87a) are connected to the relay, i thought it should work since its NC but no dice. ------------- Noob Forever ....
Posted By: aponizuma
Date Posted: August 28, 2012 at 9:25 AM
i have been reading up some more on relays and, i think, there is some serious breach in my units - i found this from another site:
i checked the schematic on the side of mine, and -
there are two (2) 87s and no 87a, both are NO. i don't think this a fluke but never thought and saw that something like this exist before? ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 28, 2012 at 12:57 PM
Oh yes there are two types the one shown and another 87b with isolated outputs.
Hopefully that might solve the problem.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 28, 2012 at 6:36 PM
howie ll wrote:
Oh yes there are two types the one shown and another 87b with isolated outputs.
Hopefully that might solve the problem.
i am sorry sir but i do not understand anymore, what will solve what problem? and i do not know any 87b, could you kindly please elaborate? ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 28, 2012 at 6:46 PM
The lower photo is the wrong relay, 87a (upper photo) is the one you want.
That is the "normal" or default SPCO type relay.
87b is just like the one shown in the lower photo but with isolated (87 and 87b) terminals as I explained above.
85 = (-) coil
86 = (+) coil
30 = common
87 = NO
87a = NC
87b = isolated NO
Google automotive relay types, Bosch/Tycho, Panasonic, Omron etc.
Also Google ISO automotive terminal letter designations.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 28, 2012 at 7:08 PM
howie ll wrote:
The lower photo is the wrong relay, 87a (upper photo) is the one you want.
that is what i thought :( the root of all evil. thank you sir for clarifying, i will now hunt for the right one and hopefully there will be no other issues with a simple project like mine. ------------- Noob Forever ....
Posted By: howie ll
Date Posted: August 28, 2012 at 7:15 PM
BTW, there's also type 88 terminals 
Sorry I had to!
The regular 5 pin is referred to as a Bosch/Tycho type "B" format cube (1" x 1" x1").
2 x 87 = twin output and 87b isolated twin output. ------------- Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: August 28, 2012 at 11:06 PM
i never thought it would be this hard to find the right relay, i asked 10+ auto supply shops today and none of them carry the configuration i need :( sir is there a way to wire the wrong relays i have together and make one reverse itself when power is applied to the coil i.e, turn off or become NC?
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Noob Forever ....
Posted By: howie ll
Date Posted: August 29, 2012 at 1:28 AM
No!
The 5 pin 87a is the standard default relay.
Go to a car breaker yard.
UK eBay was offering a 20 pack for £0.75 each, = US$ 1.10 each.
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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: aponizuma
Date Posted: September 12, 2012 at 8:06 AM
finally! found the right relay and got my simple mod to work -
thank you so much sir for all the help! now i am going to find some use to my wrong relays :) ------------- Noob Forever ....
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