switching drls

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.

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.

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.

And here's how to run the fogs properly and legally:- fogs.bmp

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.

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.

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

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

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?

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