rvehock

I am a member of the MDX forum and the post below talks about the potential problems with the way most of you have rewired their fog lights, anyone have any comments?

I hate to bring this up, but this Mod could cause very serious problems. Connecting Red/Black wire to the Wht/Red wire connects 2 different circuits fused by 2 different sized fuses. The fuse for the Red/Black wire is 15a fuse 10 (this is the fuse for most running lights and the Multiplex control unit) on the passenger's side. The fuse for Wht/Red is a 20a fuse 43 (this is the fuse for the right side headlamps). Adding these 2 values together brings you up to 35amps. That means when the headlights are on you have 2 paths to get 12volt power at a total of 35 amps. This could be very dangerous if a component shorted out or drew too much current. The wires could overheat and start a fire, or you could damage the Multiplex Controller. This mod would be better if you cut the Wht/Red wire and used one of the Scotch-lock connectors to connect the switch end of the Wht/Red wire with the Red/Blk wire. That would acomplish what you want without cross wiring the circuits. You would need to insulate the cut end of the Wht/Red wire. Should work fine that way. For those that have cross wired the circuits, simply cut the Wht/Red wire past your connection and insulate both sides and you should be good! Never just tie 2 circuits together, you are inviting trouble.


Greg in Atlanta

turbox777

uh oh.......... crap

rvehock

I went and cut the red/white wire and taped off both ends as suggested by Gregc in the above post and everything is working fine.

TL909

So, after the connection the Red/White wire won't be connected to anything?

StreetEffectz

Who even came up with doing it that way? When I rewire the fogs, I always run a seperate wire to the ignition and fuse it....just twisting some wires together is a big NO NO

TL909

So what is the correct way of rewiring the fogs?

rvehock

That is correct

rvehock

Here is the original instructions for re-wiring fogs and the replies as to the potential problem:

__________________________________________________ __
Here are the original instructions:


Rewiring Fogs

Procedure:
1. Remove cover from driver's side fuse panel. This cover is the entire end-piece of the dash. You need to open the driver's door fully to properly access this panel. It is held in place only by pressure clips. Simply pull up and out at the very bottom to start the loosening process. Gently apply pressure to the side closest to the driver and the top and the whole cover will pop out. Notice there is a long ridge on the side closest to the firewall. Make sure that side goes in first when putting the cover back on.

2. Loosen left side of driver's underdash kick panel. Although you could remove this whole piece, you only have to loosen the left side near the fog light switch to do this mod. Looking in though the opening you just made with the cover removal, you should see two brass-looking phillips-head screws. One is close to the front of the dash, one is down behind some wires holding a long thin brace in place, closer to the firewall. This is the screw you need to remove. It is the *only* screw that holds the driver's side underdash kick panel in place. Once you've removed the screw, you can loosen the left portion of the underdash kick panel by gently pulling on the piece. There are two clips at the top front, close to the bottom of the gauge cluster. You pop these clips out and the left side will come away from the dash. *This is as far as you need to remove the underdash kick panel.*

3. Unplug wiring harness to dash light dimmer switch. This is a simple plug harness that is indexed so it only goes back one way--no need to remember how it went in. This gets the cables more free for the next step.

4. Remove the fog light switch from the dash. Easiest way is to reach in from the side and grab it gently from behind (sounds like some of my dates). Squeeze gently top and bottom and push forward (towards where driver sits). The switch should pop out and be hanging by its wiring harness. Unplug the wiring harness. Press the tab in on one side of the harness and pull gently out. Set the switch aside and push the wiring harness back through the opening and bring it out through the side so you can work on it easier.

5. Spice the wires. The wiring harness consists of an inline, 5-prong plug, which is connected by five 18-20 gauge wires that are individually exposed for about an inch and then are bunched together by some rubber conduit tubing. Take the scissors or razor knife and carefully cut open the tube to expose more of the wires. You need to cut back about two inches, because you're going to want about three inches of slack to work with. Once you've cut the tubing, fan all the wires flat. You have five wires going to the harness. They are:

1. White/Blue - Ground side of indicator light (green light that shows fogs are on)
2. Blue/Red - Power to passenger side footwell relay
3. White/Red - Power from headlight switch
4. Red/Black - Power from taillight relay
5. Red - Connection to dash light brightness controller

Wire number 4 provides power to the icon on the switch whenever the lights are on (parking lights/taillights are all on one circuit). Wire number 3 provides power through the fog switch *only* if it detects the headlight switch in the low-beam position. So what we do is splice wires 3 and 4 together, thereby bypassing the headlight switch altogether. Now, whenever the taillights have power, so will this leg of the switch and the fogs will come on when the switch is pressed.

You can use whatever means you wish to join wires 3 and 4 together. Just remember you *don't* want to cut them, just splice the two together. I highly recommend an inline automotive wiring splicer (the kind that looks like a double-barrel shotgun from the end). These types of splicers are meant to be slid on over an exisiting attached wire and a second wire's free end is slid into the other side of the connector. The connector is then crimped and the latch cover is closed. However, because both of these wires are connected at both ends, if you use this type of connector you will need to drill out or punch out the solid end of the connector so both sides are completely open on each end. Then simply slide the wires into the connector, crimp the metal blade down through the wires and snap the plastic retaining tab closed. If you're good with solder you can solder in a jumper between wires 3 and 4, but that makes the mod much more permanent. I strongly recommend a two-wire inline connector and crimp.

6. Reassemble the fog light switch. Take the wiring harness from the side and push it back through the hole in the dash where the switch goes. The wiring harness for the dash light dimmer control is sort of tied with this one so you have to make sure you keep them separate and only push the fog light harness through the hole. Snap the wiring harness onto the fog light switch (it can only go one way). Then gently push the fog light switch back into the dash opening (make sure it is right-side up--green light on top, icon on bottom).

7. Replug the wiring harness into the dash light dimmer switch. Self explanatory.

8. Reattach underdash kick panel by pushing gently in area of the clips until they snap into place (remember there are two at the top, just under the gauge cluster)

9. Replace the phillips screw in the brace for the dash panel.

10. Replace driver's side fuse panel cover. Remember to start it by inserting the side closest to the firewall first. It just snaps into place.

__________________________________________________ __
Here is the replies to the above re-wiring instructions:


I hate to bring this up, but this Mod could cause very serious problems. Connecting Red/Black wire to the Wht/Red wire connects 2 different circuits fused by 2 different sized fuses. The fuse for the Red/Black wire is 15a fuse 10 (this is the fuse for most running lights and the Multiplex control unit) on the passenger's side. The fuse for Wht/Red is a 20a fuse 43 (this is the fuse for the right side headlamps). Adding these 2 values together brings you up to 35amps. That means when the headlights are on you have 2 paths to get 12volt power at a total of 35 amps. This could be very dangerous if a component shorted out or drew too much current. The wires could overheat and start a fire, or you could damage the Multiplex Controller. This mod would be better if you cut the Wht/Red wire and used one of the Scotch-lock connectors to connect the switch end of the Wht/Red wire with the Red/Blk wire. That would acomplish what you want without cross wiring the circuits. You would need to insulate the cut end of the Wht/Red wire. Should work fine that way. For those that have cross wired the circuits, simply cut the Wht/Red wire past your connection and insulate both sides and you should be good! Never just tie 2 circuits together, you are inviting trouble.

The step number 5 needs to be changed.

5. Splice the wires. The wiring harness consists of an inline, 5-prong plug, which is connected by five 18-20 gauge wires that are individually exposed for about an inch and then are bunched together by some rubber conduit tubing. Take the scissors or razor knife and carefully cut open the tube to expose more of the wires. You need to cut back about two inches, because you're going to want about three inches of slack to work with. Once you've cut the tubing, fan all the wires flat. You have five wires going to the harness. They are:

1. White/Blue - Ground side of indicator light (green light that shows fogs are on)
2. Blue/Red - Power to passenger side footwell relay
3. White/Red - Power from headlight switch
4. Red/Black - Power from taillight relay
5. Red - Connection to dash light brightness controller

Wire number 4 provides power to the icon on the switch whenever the lights are on (parking lights/taillights are all on one circuit). Wire number 3 provides power through the fog switch *only* if it detects the headlight switch in the low-beam position. So what we do is splice wires 3 and 4 together, thereby bypassing the headlight switch altogether. Now, whenever the taillights have power, so will this leg of the switch and the fogs will come on when the switch is pressed.

You can use whatever means you wish to join wires 3 and 4 together. Just remember you do need to cut the White/Red (wire3) wire about 2 to 3 inches from the connector, on the switch side splice the White/Red wire to the Red/Black wire (wire4). I highly recommend an inline automotive wiring splicer (sometimes called a Scotch-lock connector). These types of splicers are meant to be slid on over an exisiting attached wire and a second wire's free end is slid into the other side of the connector. The connector is then crimped and the latch cover is closed. . Then simply slide the wires into the connector, crimp the metal blade down through the wires and snap the plastic retaining tab closed. If you're good with solder you can solder in a jumper between wires 3 and 4, but that makes the mod much more permanent. I strongly recommend a two-wire inline connector and crimp. Be sure to Tape up the exposed end of the White/Red wire (wire 3) that was cut. Also I included a picture of a Scotch-lock connector...Hope this helps and keeps everyone safe!

TL909

Thanks for the help.

randomwalk101

I currently have a Scotch lock (drill out the other side) and used that to connect the two wires (3 & 4) together...so now all I have to do is cut wire #3 at the far end (toward the engine) and tape that end up and that should do the trick right???

Alexxx

I did it with a solder and insulated the wire with electric tape

pianoman41

Hi,

As the inventor of the original fog mod, I thought I would chime in about this observation. Although the basis of this theory certainly looks interesting on paper, it does not take into account how 12V DC circuits work in an automobile. Having two legs of DC power to a device, each fused at a different amperage, does *not* allow the device to receive either (a) more power, or (b) more amps. You cannot "sum" the two fused amp amounts together to deduce that the circuit is now fused at 35A. This is 100% incorrect. If you have two inline fuses in the same circuit path (as we do here), what happens is the entire joined circuit is now fused at the *lesser* of the two fuses' amperage ratings. In the instance of the fog mod, with the circuit now protected by both a 15A and a 20A circuit, the entire set-up is protected by the lesser, or 15A fuse. Why? Since both power feeds are in effect tied together by the splice, it is one circuit. If there is any overload or direct short on the circuit, the 15A fuse will be the one first to blow, followed shortly by the 20A. In a direct short situation, they will both almost certainly blow instantaneously. There is no danger of overloading the circuit with too many amps, since we are not changing the amount of amps in the circuit. If anything, we would expect the 15A fuse to blow with the addition of the other circuitry, but as dozens who have done this mod already can attest to, it does not.

This fog light re-wire mod is still perfectly safe, as is, although if it will make you sleep better at night, go ahead and make the further modification. Just keep in mind that this makes the mod pretty much permanent, whereas my original splice can be undone quite easily.

randomwalk101

Whew..i'm glad I haven't touched anything since it's dark...was waiting until tomorrow. I guess "tomorrow will never comes"..hehe

Lew

sooOoOo... bottom line is it's SAFE, right?

i'm guessing no one has any problems with the original mod?

DivinDude

Actually .. Piano man was correct up until he made the statement about both circuits being fused at the lower of the two fuses. In effect you have two power sources feeding the same combined circuit. Obviously, since one of the original circuits was fused lower than the other, it can be deduced that the wiring for that circuit is smaller than that of the higher fused circuit.

Now, if there is a dead short somewhere in the new circuit, it is true that both fuses "SHOULD" blow. However, if there is simply an over-load condition, such as the original smaller circuit drawing 18 amps, it cannot be assumed that the circuit will be protected by the 15 amp fuse since the 20 amp fuse can still power the circuit. Under these circumstances, the smaller wiring of the original 15 amp circuit may overheat and burn.

The only way to properly protect the circuits with the original wire alteration, is to put an inline 15 amp fuse in between each circuit (via the jumper wire). That way, the original 15 amp circuit is still protected at 15 amps and the 20 amp circuit could not pull more than 15 amps through the 15 amp circuit should the 20 amp fuse blow.

-Andy

copland007

My circuit theory is a little rusty, someone help me out. Which one below best describes the fog mod wiring:

Contestant #1:


...or...

Contestant #2:


If it is #2, than yes, the sum of the fuses would be the correct equation (note fuses of different amounts in parallel usually isn't cool)

If it is #1, than pianoman is dead on

69tl

so....come on people, which is which??

I will dig up some of my old book and see what i can find out about this...be back shortly

pianoman41

It's a lot more complicated than Matt's drawings--almost like a combination of the two, since there are relays and switches in between. I diligently studied the Helms electrical schematics tonight and can confirm that the fog light mod does *not* "combine" the two circuits, except for when both the low beams and fog lights are on together. This means that when (a) the lights are all off, (b) the parking lights are on with no fogs, (c) the parking lights are on with fogs, and (d) high beams are on, both the circuits in question (headlight and running lights) are separate (and separately fused). For all intents and purposes (electrically speaking), there is no difference in fuse protection in any of the circuits than from the factory setup.

When the fogs and low beams are on together, the circuits are "tied together" through the taillight relay but since it is a relay, the power is supplied through different legs of the relay. The factory system already has two separate 20A fuses for the headlight relays (part of where the fogs get their power from). Note that this design is similar to Matt's #2 - they are in parallel - one for the left headlight and one for the right. The fog light mod does nothing to change this.

I see nothing in the current fog light re-wire mod that would make the wiring in the vehicle unsafe. And after running this mod myself for well over a year, I continue to conclude it is safe.

stiletto

Right on Matt!!!

performed the mod this weekend (even after pounding the two fourties against all indicated instructions). Took about ten minutes ('cause I had to read the instruccions twice). Put everything back rattle free. No permanent damage done. Been wanting to do this since I got the car... if I had known it was this easy... lol. :p

stiletto

Also, just noticed that even though the stalkswitch is in the parking light position, if you pull it to alternate between high and low beams (mind you, headlights off, just parking lights on), the fogs go off or on.

I guess that is the proper behaivior. It just made me pause a bit, 'cause I did not think the high-low issue was a situation when the lights are in the parking light position...

whatever. I am bored. can you tell?

njtls

could i get a link to the oringinal fog light mod please

pej7445

Could it be said that you could use this mod and run the car with parking light/fog lights all the time as Daytime Running Lights?

I assume that the auto off feature still works in the 'parking light' selected mode.

This mod would solve my DRL needs.

Thanks for your thoughts...

stiletto

yes.

yes.

yes.

you are welcome.