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05-Z71
I have an '05 Z71 Tahoe, and I was about to do the posted fog light mod that allows your fog lights to stay on with the high beams; however, I don't want to have my fog lights on every time my headlights come on (basically bypassing the dash switch).

I was wondering if anyone has disconnected the "trigger" wire that shuts the fogs off when the high beams light up, or if there is anyone that could point me in the right direction. The desired result would be to have the fog lights COMPLETELY controlled by the dash switch, no matter what set of headlight beams is on. There's gotta be somethin simple that someone here has tried (or at least heard of) dry.gif . This concept might also eliminate another relay and ANOTHER fused wire going to my battery junction. Thanks!

PS: If anyone has a wiring schematic for that circuit from a shop manual---I would be able to go off of that.
bwhite12
I have the mod on the lights. What I did was put a switch under the dash that controlled the ground wire on the relay. That way all I had to do was bring one wire to the dash. That way I can flip the switch under the dash and the lights work as stock, or flip the switch and all lights come on with the high beams.
05-Z71
I thought about doing that too...but there's gotta be a different/simpler way. It seems that the relay closes when it gets signal from the switch, and then opens when it gets a signal from the high beams. I'm trying to avoid running wires & relays etc. Any other suggestions??
Rollin Thunder
QUOTE(05-Z71 @ Nov 18 2008, 10:27 PM) [snapback]234744[/snapback]

I thought about doing that too...but there's gotta be a different/simpler way. It seems that the relay closes when it gets signal from the switch, and then opens when it gets a signal from the high beams. I'm trying to avoid running wires & relays etc. Any other suggestions??



I dont understand why people spend 20 sometimes 30 bucks on the mod. when I went to radio shack and for 1.55 I got two diodes and put them on the on the fog,low and high relay. put it on the 85 part of all relays.
05-Z71
but in any of these cases you lose control of your factory switch! I fully understand that you can use diodes, relays, or a nuclear power plant power grid switch with 20 sequencing relays to turn on the fog lights, but I'm asking if and how to defeat the problem at the source, in order to maintain full control of the pushbutton switch that GM so graciously put in the dash.

I'm getting the feeling that this hasn't been approached before....so the question now becomes "can anyone get me a schematic of the circuit?" Thanks thumbsup.png

[attachmentid=9373]
Rollin Thunder
QUOTE(05-Z71 @ Nov 19 2008, 12:53 AM) [snapback]234769[/snapback]

but in any of these cases you lose control of your factory switch! I fully understand that you can use diodes, relays, or a nuclear power plant power grid switch with 20 sequencing relays to turn on the fog lights, but I'm asking if and how to defeat the problem at the source, in order to maintain full control of the pushbutton switch that GM so graciously put in the dash.

I'm getting the feeling that this hasn't been approached before....so the question now becomes "can anyone get me a schematic of the circuit?" Thanks thumbsup.png

[attachmentid=9373]



My guess would be to somehow. Wire a seperate switch. Powered by the battery. That can be turned on an off, no matter what lights you have on. But im the wrong person to talk to about electrical mods. wacko.gif
eugene
the schematis is available from www.gmupfitter.com

The reason people do the diodes is there isn't a simple control wire. The push button on the dash goes straight to the BCM and the BCM controls the relays. So the programming in the BCM turns off the fog relay when the higs are on. What you would have to do is replace the switch with a push on/push off instead of a momentary (could use the guts from a truck cargo light switch maybe) and run a wire from it straight to the relay bypassing the BCM. Or keep the same switch and create a latching circuit which takes about 4 relays then run a wire from it to the relay bypassing the BCM.
05-Z71
thanks eugene!---that's more along the lines of what I was looking for. I was figuring on just taking the output from the dash switch and running it to a relay (adds another dang relay but it might take care of it). Stupid BCM...
eugene
a single relay won't work since its just a momentary switch, you'll needa few relays to make a latching circuit or a different switch.
Andrew
whatever you could possibly need:
http://www.the12volt.com/relays/relays.asp

edit: oops, looks like they changed the site a little.... somewhere in there, there is a schematic that shows exaclty how to build a relay of any sort.... can't seem to find it though sad.gif

edit #2: found it! http://www.the12volt.com/relays/page5.asp
05-Z71
QUOTE(eugene @ Nov 19 2008, 12:05 PM) [snapback]234828[/snapback]

a single relay won't work since its just a momentary switch, you'll needa few relays to make a latching circuit or a different switch.


are you sure it's just a momentary switch? I used GM switch #15061687 for my roof rack light switch and it seems to function in the same manner as my fog light switch. Push once, lights come on...push again, lights turn off. I'm heading out to the garage w/ my multimeter to find out for sure. I'm hoping the fog light switch will operate as a push on, push off. Then, I'll clip the switched lead from the plug and send it to a relay. I'll be back in a few!

[attachmentid=9395]
Rollin Thunder
QUOTE(05-Z71 @ Nov 19 2008, 10:18 PM) [snapback]234992[/snapback]

QUOTE(eugene @ Nov 19 2008, 12:05 PM) [snapback]234828[/snapback]

a single relay won't work since its just a momentary switch, you'll needa few relays to make a latching circuit or a different switch.


are you sure it's just a momentary switch? I used GM switch #15061687 for my roof rack light switch and it seems to function in the same manner as my fog light switch. Push once, lights come on...push again, lights turn off. I'm heading out to the garage w/ my multimeter to find out for sure. I'm hoping the fog light switch will operate as a push on, push off. Then, I'll clip the switched lead from the plug and send it to a relay. I'll be back in a few!

[attachmentid=9395]



When did gm start putting a seperate switch for the roof lights??? I have a silverado with them but their on when ever the parking lights are on. Just curious. Sorry to take this off toppic.
05-Z71
OK, so here's what happens at the fog light switch:

1.) The control wire is the green wire with a white stripe (plug terminal B ).
2.) It has 12V at all times, until you turn the fog lights on---then the voltage goes to 0V. The voltage in that wire returns to 12V when the high beams are turned on (shutting the fog lights off again).

Now I need to find out how to make this work the way I want it to... bashing.gif

Here's a pic of the back of the switch.
[attachmentid=9396]

05-Z71
QUOTE(Rollin Thunder @ Nov 19 2008, 10:21 PM) [snapback]235024[/snapback]

QUOTE(05-Z71 @ Nov 19 2008, 10:18 PM) [snapback]234992[/snapback]

QUOTE(eugene @ Nov 19 2008, 12:05 PM) [snapback]234828[/snapback]

a single relay won't work since its just a momentary switch, you'll needa few relays to make a latching circuit or a different switch.


When did gm start putting a seperate switch for the roof lights??? I have a silverado with them but their on when ever the parking lights are on. Just curious. Sorry to take this off toppic.


Sorry for the confusion...I used this switch for my rear facing roof rack light install. To my knowledge, this switch is for trucks equipped with a snow plow option? Here's a link to the thread where it is discussed LINK
Rollin Thunder
QUOTE(05-Z71 @ Nov 19 2008, 11:57 PM) [snapback]235035[/snapback]

QUOTE(Rollin Thunder @ Nov 19 2008, 10:21 PM) [snapback]235024[/snapback]

QUOTE(05-Z71 @ Nov 19 2008, 10:18 PM) [snapback]234992[/snapback]

QUOTE(eugene @ Nov 19 2008, 12:05 PM) [snapback]234828[/snapback]

a single relay won't work since its just a momentary switch, you'll needa few relays to make a latching circuit or a different switch.


When did gm start putting a seperate switch for the roof lights??? I have a silverado with them but their on when ever the parking lights are on. Just curious. Sorry to take this off toppic.


Sorry for the confusion...I used this switch for my rear facing roof rack light install. To my knowledge, this switch is for trucks equipped with a snow plow option? Here's a link to the thread where it is discussed LINK


Im not sure I have the snow plow packedge on the hd. But it has those lights on the roof and fender. But they come on with the parking lights. Maybe they were added by the old owner?
05-Z71
QUOTE(05-Z71 @ Nov 19 2008, 10:47 PM) [snapback]235030[/snapback]

OK, so here's what happens at the fog light switch:

1.) The control wire is the green wire with a white stripe (plug terminal B ).
2.) It has 12V at all times, until you turn the fog lights on---then the voltage goes to 0V. The voltage in that wire returns to 12V when the high beams are turned on (shutting the fog lights off again).

Now I need to find out how to make this work the way I want it to... bashing.gif

Here's a pic of the back of the switch.
[attachmentid=9396]



Out of curiosity, I disconnected the green/white stripe "control" wire from the plug and tried the lights again (hoping that the fogs would stay on).....didn't work. The lights functioned as they did before---so in terms of operation, the green wire did nothing. I probed the other wires in the harness and couldn't find any voltage changes as the button was pressed. How the heck is the switch signal getting to the relay to turn the lights on & off?!?! Getting confused now. I looked at the link above that said there were wiring schematics...but there weren't any. I'm almost desperate enough to go & buy a Chilton manual, unless someone would be willing to scan the electrical schematic for the lighting circuits and send it to me? beg2.gif
Andrew
i just re-read ur original post and think i have the answer (i was a little confused the first time around)

if i'm reading it correctly and it is safe to assume that you ALWAYS want the fogs on when the highs are on, then the solution is simple.

splice into the high beam hot wire and connect it to the switched hot wire (the one that leads to the 85 post of the relay) of course, to keep from overloading your fog light switch u'll need a diode in the splice


edit: i found the diagrams that i was looking for in my previous post.... check it again wink.gif
05-Z71
QUOTE(Andrew @ Nov 19 2008, 11:41 PM) [snapback]235045[/snapback]

i just re-read ur original post and think i have the answer (i was a little confused the first time around)

if i'm reading it correctly and it is safe to assume that you ALWAYS want the fogs on when the highs are on, then the solution is simple.

splice into the high beam hot wire and connect it to the switched hot wire (the one that leads to the 85 post of the relay) of course, to keep from overloading your fog light switch u'll need a diode in the splice


edit: i found the diagrams that i was looking for in my previous post.... check it again wink.gif



Andrew, I think we're on the right track here. To clarify again, I do NOT want the fogs to come on every time my low beams come on (which is what happens when you do the fog light mod posted on the site). However, when I do decide to use the fog lights, I want to turn them on with the push button switch and have them stay on...even if I turn on the high beams. Then, if I choose, I will be able to push the switch button again and shut them off.

I would've done the fog mod posted on the site already, if I didn't lose control of the fog lights. I just want to be able to turn the lights on & off whenever I want, but have them stay on when I turn on the high beams.

Thanks for the help! I might be contacting you to get more details when I give this a shot (providing it will absolutely work)
IMI4tth3w
i would have looked up the wire schematics already but i lost my chiltons =( guess i'll go have to buy a new one.

i know exactly what your talking about from the beggining.

donno if this tidbit will help, but the way chevy works the highs and lows is when the car is on with the regulars on, the both wires going into the highs come up with 12V. when the highs are on, both wires to the regs switch to 12V instead of one 12V one 0V.

it may be somewhat the same with the fogs. but i'll have to double check that. i'll see if my buddy is awake and can log me into alldata.com
05-Z71
thanks much! I'm thinking that the idea that andrew proposed might be the trick that I'm looking for. I just need to check on the diode situation (have to pull out my circuits book from school alberteinstein.gif ) I'm still interested in a schematic if you get around to it. Later!
IMI4tth3w
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there ya go! gotta love alldata and friends with passwords
IMI4tth3w
whoops thats the relay diagram for mine, which is a 2000 lol. here's the 05 one.

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IMI4tth3w
i took a long hard look at this. not sure what your gonna have to do, but i'm pretty sure what your looking for/need to do is something to do with the 2 wires i connected with the red line.

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HokieNav
QUOTE(Rollin Thunder @ Nov 20 2008, 12:04 AM) [snapback]235036[/snapback]

Im not sure I have the snow plow packedge on the hd. But it has those lights on the roof and fender. But they come on with the parking lights. Maybe they were added by the old owner?

Two different kinds of lights - you're talking about the 5 cab clearance lights across the roof. They are designed to work with your parking lights.

That switch is meant to control a roof mounted strobe or rotating warning light, as usually found on snow plows (why it's included in the snow plow prep package) or other work trucks.
eugene
that switch is different internally, it is a push on / push off, the fog is momnetary.

http://www.gmupfitter.com/publicat/2004_BB...Electric_CK.pdf

p 242 shows the relay side under the hood, p 262 shows the switch, however from the schematics you can't really tell its just momentary, but if you still don't want to beleive me open it up and see or put your meter on pins c and d.
mrl112
1. There's no way to do this without adding some kind of other wire or relay unless you reprogram the BCM.

2. Run a relay under your hood, so you don't have any other dash switches that uses the high power wire as the trigger for the fogs. Then anytime your highs are on, your fogs will automatically come on (if they weren't on) or stay on (if they were on.) When your highs are off, you still maintain nomal, complete control of the fogs with the dash switch.

I think you're making this significantly more complicated than it is. tongue.gif
05-Z71
yah...I think I might as well throw in the towel on the whole idea---I think I'll be able to deal with the situation that y'all have described. I plan on having my low beams on 90% of the time anyways---so I'll have control of my fogs at least 90% of the time dry.gif Thanks to everyone for the input! If someone thinks of anything else---please let me know. Later!

PS: I think I'm going to give the diode trick a try.
Scott
I'm sure many of you are aware I'm not a big fan of diodes for a couple of reasons, but I won't preach. If I was going to go that route, I would do it on the back side of the fuse box, tapping into the wires directly, and shrink wrapping everything, including the diode securely. Realizing how much time that takes, Imho, it's just easier to go the relay route, which is why I've always felt that was the best solution. As such, our FAQ write up all head in that direction.
mrl112
QUOTE(05-Z71 @ Nov 20 2008, 07:48 PM) [snapback]235247[/snapback]

yah...I think I might as well throw in the towel on the whole idea---I think I'll be able to deal with the situation that y'all have described. I plan on having my low beams on 90% of the time anyways---so I'll have control of my fogs at least 90% of the time dry.gif Thanks to everyone for the input! If someone thinks of anything else---please let me know. Later!

PS: I think I'm going to give the diode trick a try.

I guess what I don't understand is why you would want to turn off your fogs with your fogs if you wanted to take the time to have them come on with the highs in the first place. huh.gif BUT, you'll be very happy with the mod. I love having my highs/lows/fogs all on when I hit the highs. It throws tons of light down the road!
05-Z71
QUOTE(mrl112 @ Nov 21 2008, 10:02 AM) [snapback]235354[/snapback]

QUOTE(05-Z71 @ Nov 20 2008, 07:48 PM) [snapback]235247[/snapback]

yah...I think I might as well throw in the towel on the whole idea---I think I'll be able to deal with the situation that y'all have described. I plan on having my low beams on 90% of the time anyways---so I'll have control of my fogs at least 90% of the time dry.gif Thanks to everyone for the input! If someone thinks of anything else---please let me know. Later!

PS: I think I'm going to give the diode trick a try.

I guess what I don't understand is why you would want to turn off your fogs with your fogs if you wanted to take the time to have them come on with the highs in the first place. huh.gif BUT, you'll be very happy with the mod. I love having my highs/lows/fogs all on when I hit the highs. It throws tons of light down the road!



I would prefer to not have them turn on until I want them on (with the switch) but there doesn't seem to be a way to do that because of the BCM. I'll have to deal with them coming on with the highs---no big deal tho. I usually turn them on at night anyways because they light up right in front of the truck, and fill in road up to the low beam pattern.

As far as Scott's concern---I'm aware of your diode dislike after reading all of the threads on the topic tongue.gif Your reasons are valid. I agree that the "right" way to use the diodes would be to wire them in under the fuse box (which I am willing to do). I have the perfectionist disease that my father (also an engineer) passed down to me. The reason I don't want to use another relay is because I have alot of crap tapped into that battery junction as it is (roof rack light, 4-way headlight, amplifier)--it's getting pretty crowded. You can rest assured that if I use the diodes---I'll make sure to do it the right way thumbsup.png !

Does anyone know which end of the diode goes to which terminal? Diodes have a forward & reverse bias to block/allow current flow in one direction---which end goes where? Or does that only apply to AC circuits....
mrl112
QUOTE(05-Z71 @ Nov 21 2008, 01:13 PM) [snapback]235412[/snapback]

Does anyone know which end of the diode goes to which terminal? Diodes have a forward & reverse bias to block/allow current flow in one direction---which end goes where? Or does that only apply to AC circuits....

You want it facing so that the current will travel from the high wire to the fog wire. I have never used a diode, but was going to do this to my Blazer, and remember that the diode had an arrow or something of the sort to show which way the current was supposed to flow.
hunter
Diodes have a stripe (usually silver). This should go toward the fogs. To double check use a multimeter.

Digital multimeters have a special setting for testing a diode, usually labelled with the diode symbol.
* Connect the red (+) lead to the anode and the black (-) to the cathode. The diode should conduct and the meter will display a value (usually the voltage across the diode in mV, 1000mV = 1V).
* Reverse the connections. The diode should NOT conduct this way so the meter will display "off the scale" (usually blank except for a 1 on the left).
05-Z71
Thanks alot hunter & MRL--- I'll see what I can do. Now...how to remove the fuse box under the hood...I'll give the site a search, otherwise, I'm sure I'll figure it out. I'll let you know how it turns out!
mrl112
QUOTE(05-Z71 @ Nov 21 2008, 04:53 PM) [snapback]235461[/snapback]

Thanks alot hunter & MRL--- I'll see what I can do. Now...how to remove the fuse box under the hood...I'll give the site a search, otherwise, I'm sure I'll figure it out. I'll let you know how it turns out!

I got mine most of the way out and was able to route whatever I was routing (amp power maybe.) It's held on with either a few bolts or a few plastic clips. Either way, it's easy to figure out and remove. thumbsup.png
OmarR
QUOTE(hunter @ Nov 21 2008, 11:24 AM) [snapback]235430[/snapback]

Diodes have a stripe (usually silver). This should go toward the fogs. To double check use a multimeter.


The way the diode faces will depend entirely on how you are wiring up the system.

If you are using the diode method, and NOT the "adding a relay" method, then you should be activating the negative leg of the stock relay. This is the way the BCM does it. So in this case, you will want the stripe facing away from the fog lamps.

AGAIN, there are different ways to wire up the diode, but this is the easiest and simplest way to do it.
05-Z71
QUOTE(OmarR @ Nov 24 2008, 10:37 PM) [snapback]235910[/snapback]

QUOTE(hunter @ Nov 21 2008, 11:24 AM) [snapback]235430[/snapback]

Diodes have a stripe (usually silver). This should go toward the fogs. To double check use a multimeter.


The way the diode faces will depend entirely on how you are wiring up the system.

If you are using the diode method, and NOT the "adding a relay" method, then you should be activating the negative leg of the stock relay. This is the way the BCM does it. So in this case, you will want the stripe facing away from the fog lamps.

AGAIN, there are different ways to wire up the diode, but this is the easiest and simplest way to do it.


If I do this I want to do it right. Do you have a diagram that would show what goes where, and which polarity etc. I'm heading to RadioShack sometime this week to get the components. Thanks for the input!
eugene
GM does some positive switched and some negative switched for different circuits. It doesn't really matter depending on which way you look at current flow. Conventional current flow is from positive to negative but electron flow is negative to positive, one of the first electronics classes toward an electronics engineering degree will go into it in great detail about why the direction doesn't matter conventional current flow is just what people are more familiar with, it wasn't until they were able to produce microscopes that could see down small enough they noticed the elctrons actually flow negative to positive and the missing electron or holes from positive to negative. So switching positive or negative each had their advantages and disadvantages.
05-Z71
just thought I'd add onto this thread with an update. I got bored tonite and finally wired my fog lights so that they stay on when the high beams are on. It turns out that if you use the diode method, you need to have the polarity stripe TOWARDS the high beam relay leg. It works GREAT and I've got pictures if anyone is interested. I used a dremel to grind a little bit of material away from the relay case. This allows the relay to sit flush like it always did because the wire attaching to the terminal leg fits up into the little "notch" that I made.

The reason I used the diode method is because I have too dang many wires going into my power block under the hood. I didn't want to use any more relays and this was just easier for me. It works great, and I'll eventually wire it in on the bottom side of the fuse panel so the diode is not visible. Just wanted to make sure it all worked first. thumbsup.png
Rollin Thunder
Does it look like this??? LOL I used the diode method just cause I didnt feel like wireing a bunch of crap. Plus they were like 2 bucks at radio shack. So I did the 6 high mod. super simple.

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obert272
I want to do the diode mod but I need pics of how you do it. I have a lot of wires so I think the diode method would work better.
Rollin Thunder
QUOTE(obert272 @ Jan 25 2009, 01:41 PM) [snapback]250004[/snapback]

I want to do the diode mod but I need pics of how you do it. I have a lot of wires so I think the diode method would work better.


http://www.tahoeforum.com/showthread.php?t=12905 good.gif
obert272
Thanks good writeup. i might do this!
05-Z71
i'm not dissing rollin thunder's method, but jamming diodes into the sockets prolly isn't the best way. If you're good w/ a solder gun then I would recommend making a solid connection, otherwise, I would stick to the relay method. I'll post some pics later tonite or tomorrow of my set-up. I soldered the diode in and it was quick & easy. A mechanically and electrically solid connection will make your life easier down the road. thumbsup.png
retrofit
QUOTE(IMI4tth3w @ Nov 19 2008, 10:50 PM) [snapback]235062[/snapback]

IPB Image

there ya go! gotta love alldata and friends with passwords

any chance of someone posting a 2001 headlight digram? (above is the fog lights) thanks
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