How To: Auto Fog Lights (Don't Have To Push Button)

midwestdenaliguy · August 9, 2018

I posted this in another thread, but they were looking to only have the fogs on with high beams. My solution has the fog lights automatically turn on, and stay on, anytime the parking lights or headlights come on (hi and lo beam). You never have to hit the button. Figured I'd label this as a "How To" in case those are housed somewhere. I'm new to this forum, so let me know if I should be doing this differently. Cheers!

Hey guys - recently bought a 2016 Sierra Denali and joined the forum. Stumbled upon this thread while clicking around. I always gain so much from these forums, so I thought I'd give back in my first post. Here is a simple solution I made to have the fog lights automatically turn on with the day time running lights - did this with my previous truck as well (2008 Cadillac Escalade). I bought a diode and used some 14 gauge wire I had laying around. I wrapped 14 gauge wire to each end of the diode and sealed it with marine grade shrink wrap (waterproof). I then got into the engine bay fuse box and pulled the fuses for the fog lights (#49) and day time running lights (#28 or #29 - can be either, only need one). When I put the fuses back in I wedged the wire in one of the slots for the fuse connector, one end of the diode/wire goes in the fog light fuse and the other goes in the DRL fuse. Keep in mind the diode is directional (only allows current one way), so if it doesn't work at first just flip the wire around. Now anytime your DRL's are on, the fog lights will automatically come on. No need to push the fog light button. The fog lights also stay on when you turn on your brights. I attached a photo of my set up, it was taken standing over the driver side fender looking at the fuse box. Ask any questions if you got em!

txab · August 9, 2018

phabejhmoob · August 9, 2018

1 hour ago, midwestdenaliguy said:

I bought a diode

Can you give more details on the diode? Where did you get it from, Radio Shack no longer in biz... Amazon? Ebay?

Edit: Also, does the fog light icon light up in the dash as if you pushed the button?

Thanks.

Edited August 9, 2018 by cs2016lt

Areth · August 9, 2018

Thanks!

midwestdenaliguy · August 9, 2018

1 hour ago, cs2016lt said:

Can you give more details on the diode? Where did you get it from, Radio Shack no longer in biz... Amazon? Ebay?

Edit: Also, does the fog light icon light up in the dash as if you pushed the button?

Thanks.

Good question on the diode, it was bought over 4 years ago when I originally did this - at Radio Shack :-). I believe I have a spare in my toolbox, I'll check after work tonight and get back. For your second question, the fog light dash icon will come on only when you hit the button, it will not display when they automatically turn on. The button essentially does nothing after you create this electrical loop. This is simply an electrical jump, so none of the computers realize anything has changed. All your icons will operate normally on the dash, with the exception of the fog light icon (which technically does function properly to display it - but it doesn't mean anything). Hope that makes sense.

sk · August 9, 2018

Nice idea. If you don't want to jam the wire down into the fuse blade you could also wire fuse taps on each end of the diode:

https://www.amazon.com/ABN-Fuse-Tap-Holder-5-Pack/dp/B01BU59RFM/ref=sr_1_9?ie=UTF8&qid=1533836911&sr=8-9&keywords=fuse+tap

midwestdenaliguy · August 9, 2018

3 minutes ago, sk said:

Nice idea. If you don't want to jam the wire down into the fuse blade you could also wire fuse taps on each end of the diode:

https://www.amazon.com/ABN-Fuse-Tap-Holder-5-Pack/dp/B01BU59RFM/ref=sr_1_9?ie=UTF8&qid=1533836911&sr=8-9&keywords=fuse+tap

Didn't know those existed! This is why I love forums...

scott.moody.9401 · August 9, 2018

Any 1N4001, 1N4002, 3,4, etc diode will work

Sent from my SM-T817V using Tapatalk

Moore84 · August 9, 2018

Solid post! Been waiting to do this. The fog lights really do light up the road at night. Adding this to my weekend to do list.

Edited August 9, 2018 by Moore84

phabejhmoob · August 9, 2018

1 hour ago, sk said:

Nice idea. If you don't want to jam the wire down into the fuse blade you could also wire fuse taps on each end of the diode:

https://www.amazon.com/ABN-Fuse-Tap-Holder-5-Pack/dp/B01BU59RFM/ref=sr_1_9?ie=UTF8&qid=1533836911&sr=8-9&keywords=fuse+tap

i use these for my dashcams on all my vehicles.

Pearl2017 · August 9, 2018

Props for the great idea/contribution!

I have not looked at the schematic so don't know, but do the fogs normally power from a relay? Concern for me would be if you are now powering the fogs piggybacked on another circuit. If there is a relay that jumper could/should be going to the energizing coil of the fogs relay. This way it is pulling power on its intended fused circuit and not doubled up on another.

On those fuse taps... Make sure you orient the tap correctly so that the LOAD is connected AFTER the fuse and not before. One leg of a fuse is BATTERY and the other leg goes to the LOAD. If you orient it incorrectly you could continue to pull power even if the fuse blows. You can find the BATTERY leg by pulling the fuse and using a voltmeter to find which pin is +12v and make sure the tap is on the other pin.

Edited August 9, 2018 by Pearl2017

phabejhmoob · August 9, 2018

2 hours ago, midwestdenaliguy said:

Good question on the diode, it was bought over 4 years ago when I originally did this - at Radio Shack :-). I believe I have a spare in my toolbox, I'll check after work tonight and get back. For your second question, the fog light dash icon will come on only when you hit the button, it will not display when they automatically turn on. The button essentially does nothing after you create this electrical loop. This is simply an electrical jump, so none of the computers realize anything has changed. All your icons will operate normally on the dash, with the exception of the fog light icon (which technically does function properly to display it - but it doesn't mean anything). Hope that makes sense.

Thanks, that would greatly help! no guessing..

midwestdenaliguy · August 9, 2018

9 minutes ago, Pearl2017 said:

I have not looked at the schematic so don't know, but do the fogs normally power from a relay? Concern for me would be if you are now powering the fogs piggybacked on another circuit. If there is a relay that jumper could/should be going to the energizing coil of the fogs relay. This way it is pulling power on its intended fused circuit and not doubled up on another.

That's a legit question, here are my thoughts:

https://www.autogenius.info/gmc-sierra-from-2014-fuse-box-diagram/

That's a link to the fuse box diagram for 2014, 2015, and 2016 Sierra's. Looking at the relay section I don't see anything for fog lights. What I can tell you is that I ran this exact set up in my 2008 Escalade for the last 4 years and didn't have a single issue - no flickering, no burning, no electrical errors/failures, etc. I've been driving the Sierra like this for a week now - day, night, rain, shine - and haven't had a single issue either. Let me state this though - I am not an electrician/technician and cannot confirm, based on electrical expertise, that this won't lead to an issue in these trucks. I have basic electrical knowledge and didn't run into any issues on my GMT900 platform vehicle for 4 years with this mod. Take that for what it's worth.

phabejhmoob · August 9, 2018

53 minutes ago, midwestdenaliguy said:

That's a legit question, here are my thoughts:

https://www.autogenius.info/gmc-sierra-from-2014-fuse-box-diagram/

That's a link to the fuse box diagram for 2014, 2015, and 2016 Sierra's. Looking at the relay section I don't see anything for fog lights. What I can tell you is that I ran this exact set up in my 2008 Escalade for the last 4 years and didn't have a single issue - no flickering, no burning, no electrical errors/failures, etc. I've been driving the Sierra like this for a week now - day, night, rain, shine - and haven't had a single issue either. Let me state this though - I am not an electrician/technician and cannot confirm, based on electrical expertise, that this won't lead to an issue in these trucks. I have basic electrical knowledge and didn't run into any issues on my GMT900 platform vehicle for 4 years with this mod. Take that for what it's worth.

if you use fuse tap, it should protect you from an overload. Which is why it's better than jumping straight with a cable.

midwestdenaliguy · August 9, 2018

20 minutes ago, cs2016lt said:

if you use fuse tap, it should protect you from an overload. Which is why it's better than jumping straight with a cable.

Yeah, those fuse taps would be cheap peace of mind. Just ordered a set that'll arrive Saturday. I'm going to install those and update my original post. Even though I didn't have an issue before, I'd feel terrible if someone followed this and it led to a major problem.

Edited August 9, 2018 by midwestdenaliguy