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Discussion Starter · #1 ·
I have a some questions about the electrical circuits for the indicator lights in the instrument cluster are configured... ...Sort of... ...Maybe(?).

The reason is that I am installing fog lights on my 03' Grand Cherokee.

It came from the Factory without Fog Lights, but it looks to me like the "Junction Block", (JB), does have all electrical conductors in the Fuse Connectors and Relay connectors installed. I am hoping that they also have wires on all of those connectors too.

I have 2 questions about the BCM regarding Fog Lights. to those of you that have, or had, a WJ with factory installed "Fog Lamps", when using the Fog Lamp Switch on the "Multi-Function Switch";

1- Do the Fog Lights come on at all when there are no headlights on?
2- If the fog lights only come on when headlights are on, do they go off when the high beams are switched on?

If the answer to number 1 is no and the answer to number 2 is yes, that would be icing-on -the-cake for me.

Anyway, I would like to know if there is anyone here that has successfully connected an auxiliary switch for the Fog Lamps to the BCM that takes place of the factory Fog Light Switch without damaging the BCM(?).

In the Service Manual, in the wiring section, (reference page 8W-50-2, (Page 847 in the Service Manual PDF I have), it shows the Multi-Function Switch with resistors; which indicates to me that there is a resistance value logic circuit sensing scheme in the BCM. The Fog Lamp Switch is number 4 in the diagram of the "Left Multi-Function Switch"

It looks like I should be able to connect an auxiliary on/off switch
between Pin 15 on C2 and pin 16 on C1 of the BCM
.


Product Rectangle Slope Font Parallel


Then, all I would hopefully have to do is plug-in a new Fog Lamp relay for that part of the circuit.

Of course, I will also have to find the actual wire coming from pin 87 on the Fog Lamp relay, trace where it goes to and make sure it has not been routed to something else, then tap into it for the + part of the circuit on new fog lights.... ...Then, of course, connect an appropriate - Ground to each Fog Lamp.

Otherwise, I would have to do more tapping with "Add-A-Circuit Holder" Connectors, (with the additional fuse), do some slightly complicated wiring and install at least one auxiliary relay.

I have pretty much figured out the wiring for the auxiliary fuses and relay/s to make it so 3 switching positions would have to be in the 'on' position simultaneously for the Fog Lights to come on:
1- Ignition on, (on only, not start or ACC),
2- Low Beam on,
3- The Fog Light Switch in 'Closed' position. I would wire it to - Ground to complete the circuit for switching one of the Relays.


However, after comparing the amount of work and the 2 possible different outcomes, I think I would rather just jump the 2 connections, cap the unused end of the "Left Multi-Function Switch", then locate and tap the wires from the Fog Lamp Relay Pin 87 of the Fog Lamp Relay to the new fog lamps I am going to install as I mentioned earlier, if I can be reasonably sure the BCM won't get damaged.
 

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The fog lights are factory wired to only come with the low beams on. they will shut off when the high beams are on. Your diagram shows you tapping into the fog lamp "Sense" wire that goes to the BCM. That is not where you should tap. The BCM also has a fog lamp relay control output which sends a ground signal to the fog lamp relay. I have included the diagrams for these circuits. The BCM is under the Junction block. The wiring in the front may already be there, just need to install the fog lights.
 

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Discussion Starter · #3 ·
Thanks for the input Gluckmysock.

An explanation before I post my next comment and questions.

1- I am going to install fog lights, and attach them to the front bumper, which, I will ask questions about in in other postings, possibly on another thread specifically related to mounting Fog Lights into an OEM bumper that did not come from the Factory, with Fog Light mounting.

2-the preferable way I want the Fog Lights to function after the install is that 3 conditions must be present for the Fog Lights to be on:

Condition 1, Rocker Switch in on position.
Condition 2, Ignition Switch in "Run" position only.
Condition 3, Fog Lights on only when low beam headlights are on when condition 1 and condition 2 are simultaneously present.

Another thing is that there has to be an indicator light in plain view of driver, preferably in the Instrument Cluster where there, hopefully, is an existing light socket for Fog Lamp on Indication that is already there and wired that would function without anything having to reprogrammed.


I am 99% sure that the way I have configured my crude diagram, that the Fog Lights will function as I expect.

Anyway, that being said, it would be nice if there was another way to avoid the extra wires, the Add-A-Circuit fuse connectors, and an additional relay etc. by simply rearranging the "Fog Lamp Switch Sense" the way I showed in my 1st post of this thread.

My next post here is coming soon.
 

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Discussion Starter · #4 ·
The fog lights are factory wired to only come with the low beams on. they will shut off when the high beams are on. Your diagram shows you tapping into the fog lamp "Sense" wire that goes to the BCM. That is not where you should tap. The BCM also has a fog lamp relay control output which sends a ground signal to the fog lamp relay. I have included the diagrams for these circuits. The BCM is under the Junction block. The wiring in the front may already be there, just need to install the fog lights.
RE:
The fog lights are factory wired to only come with the low beams on. they will shut off when the high beams are on.
Great! That is a good place to start from for trying to utilize that built-in function.

RE:
Your diagram shows you tapping into the fog lamp "Sense" wire that goes to the BCM.
Yes, that is correct.
I could be wrong, but from what I can tell, tapping into the fog lamp "Sense" wire, (as I show in the diagram), to the BCM is the only way I could come up with that could utilize the Built-In Factory Switching scheme because the controlling of the Fog Lamp switching is all connected to and through the BCM.... ...I do not see any relay wiring that would otherwise serve the same function that I believe the BCM actually does.

RE:
...the fog lamp "Sense" wire that goes to the BCM. That is not where you should tap.
OK, I get what you are saying.

Can you explain how tapping into the Fog Lamp Relay Control with a switch to ground would not bypass the factory scheme;...
...IE:
"The fog lights are factory wired to only come with the low beams on. they will shut off when the high beams are on."
function?

Yes, Gluckmysock, I have looked at those sections of the wiring diagram/s you posted and quite a few other pages that are in in my Service Manual before I asked my questions.
I really appreciate your input and help... ...Thanks!:)(y)... ...I am hoping for more.:geek:

Anyway, from what I can tell, after reading and studying the wiring diagram/s in my Service Manual that show WJ's that do have the Factory Installed Fog Lamp Switch built-in to the Left Multi Function Switch:... ...I do know that...
...To turn the Fog Lamps on, the BCM gets input via closing the contact @ #4 in the Left Multi-Function Switch for the BCM to switch the Fog Lamp Relay Control to on and, I am guessing, the functioning of the switching scheme you mentioned.

Because there is no direct Relay switching from the Low Beam Relay and the Fog Lamp Relay in the wiring diagrams, I am guessing that the BCM controlls the Fog Lamp relay switching scheme.

My WJ does not have the Fog Lamp Switch option in the Left Multi-Function Switch
, so I was thinking...

...Would it be feasible, (doable), to just install a Rocker Switch to serve as the electrical contact in the BCM circuit as if there were a Factory Installed Fog Lamp Switch 'contact' like the modified diagram I posted shows?
I know that a Fog Lamp Relay would have to be plugged-in to the JB and the Fog Lamp Wires from the Fog Lamp Fuses have to be traced and connected to each Fog Lamp. Also, the Body Grounds for each individual Fog Lamp would have to be correctly connected.

It seems to me that the configuration of my modified diagram should not introduce any Volt/Amps that is not already present in that part of the BCM switching, but, (maybe?), only IF the BCM is the same as the BCM in WJ' that do have the Factory Fog Lamp Switch. Is there a way to tell?...
...Do you know if the BCM in WJ's without factory installed Fog Lamps WJ's are the same as Installed Fog Lamp WJ's?... ...or have the correct programming?

In other words, I guess, in a roundabout way, I am, in essence, asking if I were to install a Left Multi-Function Switch that has a functioning Fog Lamp Switch from a parts WJ, to my WJ that never had one, and also installed the Fog Lamp Relay and the R & L Fog Lamp Fuses in the Fuse Box, and wired the Fog Lamps from Fuses and Ground, would it work?

My drawing skills are minimal and rather crude and I have not had the time or need to re-draw the pencil diagram, so please excuse my rather sloppy and crude wiring diagram.
Anyway, with the possible exception of the Fog Lamp Indicator light in the Instrument Cluster, I do know the circuitry in it would work as I want it to.

Also, FWIW: I included the diagram of the first wiring option I came up with that I am still considering. It does involve clipping and apping the wire of Fog Lamp Relay Pin 85 and connecting Rocker Switch going to Ground, but I would use the "Additional Relay" in the diagram, which seems to me to be necessary to have Fog Lights come on only under the 3 conditions;
Condition 1, Rocker Switch in on position.
Condition 2, Ignition Switch in "Run" position only.
Condition 3, Fog Lights on only when low beam headlights are on when condition 1 and condition 2 are simultaneously present.

White Motor vehicle Automotive design Mode of transport Handwriting


Anyway, if I decide to go the route of my 'crude' and 'sloppy' diagram shows, I still need to know what wiring options there are for the Fog Lamp Indicator Bulb in the Instrument Cluster are.
I am thinking that the wiring for the Fog Light Indicator Bulb in my diagram would not work if the trace on the circuit board of the I nsrument Cluster has Common + for the Bulb instead of Common - Ground.


I won't use an illuminated Rocker Switch for Indicator because, 1- Rocker being switched to ground makes the wiring for that much more problematic and, if at all possible, I opt to somehow have the indicator light located in the designated location in the Instrument Cluster even if I have to modify a PC74, and hard-wire an LED bulb through it.
 

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Glad I can help. I attached some more info. All gauge cluster include the bulb and wiring for fog lights. See attached. WIN!!
A replacement multifunction switch is $62.00. Multifunction switch on Amazon It would be cheaper at a junk yard.
I would believe the wiring is already there for the switch and maybe the fog lamps. manufacturers usually build all the options in the harness since it's cheaper than having a bunch of different harnesses. I can't find any diagrams showing power to the MF switch. Just a ground. so, worse case scenario, you would have to install a rocker that just grounds the fog lamp sense to the BCM. Even without foglamps, just grounding that fog lamp sense would turn the dash indicator on.
 

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Discussion Starter · #6 ·
Thanks Gluckmysock, that is the kind of info I did not have. (y) :geek:

In the write-up on the Fog Lamp Indicator, it says:
"The front fog lamp indicator gives an indication to the vehicle operator whenever the front fog lamps are illuminated.
This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Body Control Module (BCM) over the Programmable Communications Interface (PCI) data bus."
(I added the color scheme, change in Font, Text size and underlining for emphasis)

With all that to consider, at this point, unless there is an 'inexpensive' way to reprogram the PCI without having to also replace the 'cluster' to have the correct transistor programing for Fog Lamp Indicator etc, it looks like my first thought and pencil drawn diagram, ( other than the Indicator Light circuit part of it), is going to be the way to go about getting functioning Fog Lights.

Then it is a matter of coming up with a fused indicator light circuit that works, is in good view, not too bright for night driving and not too dim for daytime driving either. I am skeptical and leery :cautious: of trying to get indicator light to work with the dimmer circuit, but I suppose it would be possible to do with a second 'additional' relay, trick wiring and modifying a bulb holder. That seems like too much hassle though so I may just install a fused indicator pilot light somewhere not in the Cluster and out of the way from any potential maintenance points, but still in the driver's forward view and just be done with that part of it.

I suppose it wouldn't hurt to just put a good bulb in the socket and see if it turns on during the pre startup indicator light test sequence before cranking the engine. I suspect it will not come on because there were no Fog Lamps as it was delivered from the factory.


Still weighing the options and looking for more info.
 

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And further down the rabbit hole we go. I attached the operation of the gauge cluster. and it's a damn sophisticated piece of equipment. You may be right, and the light may not work since it didn't come with them from the start and the BCM may not have included the programming. Since the EMIC (Electromechanical Instrument cluster) can test for bulb failures, you may have to do all hand wiring. Ugh. That will suck.
 

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Discussion Starter · #8 ·
Thanks once again Gluckmysock(y)(y)

And further down the rabbit hole we go.
Ah, yes. However, with this new, to me, info, my question about what to do regarding the Fog Lamp Indicator Light in the Cluster has been indirectly answered:geek::sneaky:

The Fog Lamp Indicator Light is an integral LED component soldered onto the circuit board and therefore I will not be using any part of it for my particular application.:(:rolleyes:

Therefore, with the exception of the Indicator light, I will proceed to do as my wiring diagram shows.

The next wiring ordeal is to; locate what AWG size the Fog Lamp Relay output wire size actually is, because, According to my SM, the wire to each individual light is AWG 20 that is on a 15 amp fuse!!! :eek: :eek: :eek:... ...I will inspect and check closely for that🔍🔎.
Product Rectangle Slope Font Material property
Rectangle Font Schematic Material property Parallel

...If AWG 20 wire is the case, I will be rewiring from Relay output, (pin 87), all the way to each Fog Lamp with AWG 14 wire for the 15 amp fused circuit.

Also, I still have to look further into what my best options are going to be for the indicator light.
 

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Discussion Starter · #9 ·
Wiring Diagram has been Updated so that the Rocker Switch can be an illuminated one.

There is no reasonable way for me to utilize the front Fog Light indicator in the instrument cluster. Therefore, I have Updated my wiring diagram so that the Rocker Switch can be an illuminated one, (will be amber color), and it will be the only Fog Light indicator.

As a result of the wiring difference there will be a slight variation from the exact way I wanted it to function, but it's minimal enough of a difference, and it's okay with me.

The difference is that there will be one switching sequence where the fog lights won't be on but the rocker switch indicator will be illuminated anyway. That will occur When the ignition switch is off, low beams are on and Rocker Switch is on, the indicator light will be on, but the fog lights will actually be off.

I can most certainly live with it that way, even though it's not 'perfect' it will be well within the "good enough" parameter for me.

The Diagram with Rocker switched to ground.

Condition 1, Rocker Switch in on position.
Condition 2, Ignition Switch in "Run" position only.
Condition 3, Fog Lights on only when low beam headlights are on when condition 1 and condition 2 are simultaneously present.

View attachment 229747
The Updated Diagram with the amber colored 'illuminated', (when on), Rocker Switch.
White Motor vehicle Handwriting Organism Automotive design
 

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Discussion Starter · #11 ·
After more studying and familiarizing myself with the Service Manual's wiring scheme, I now realize that the Factory installed fog light relay is internally plugged-in to the BCM within the Junction Block so the wiring can't be altered as I had intended to do when I sketched the previous wiring diagrams.

I eventually got to the realization; that, I should have just done in the first place, what I would have done on an older vehicle, (more-less).
I am going to still use the Little-Fuse Add-A-Circuit for the fusing of the relay circuit and Ignition/On part of the circuit.
I will also use a Jumper wire on Pin 30 of the Fog Lamp Relay Plug without having any relay in that placement. Doing that will utilize Fuse 24.


Another thing is that, I will be running #14 wire from my added Relay 2 directly to the High-Temp, waterproof Fog Lamp Plugs I got for the install.

This one is not quite so crude and ugly as my previous wiring diagram sketches
.
Schematic Rectangle Font Parallel Engineering

With this scheme, the Fog Lights will not be on with the ignition off or on ACC, (I am not sure if they will blink out when cranking to start), but the illuminated Rocker Switch will indicate with the Low Beams on even though the Fog Lamps are not going to be on when the Ignition Switch is not in the "Run" position.​

I could make it so the indicator light on the Rocker Switch only goes on when the Fog Lights are actually on, but I am not going to bother running more wire and adding another relay switching circuit just for that.


'
 

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Discussion Starter · #12 ·
Update:
I have mounted the switch and tested the circuit with a Volt Meter and it does work as I described...
...However, the illuminated Rocker Switch's LED is way too bright, so I added two 10KΩ fixed resisters side by side, connected in parallel, (making 5KΩ resistance), that is in-line with the Rocker Switch's ground connection. It may still be too bright at night. If it is too bright at night, I will clip one of the resistors and see if it is bright enough in daylight.

I have run the + wire from Relay 2 behind the bumper cover where each Fog Light will be mounted. I used modified, (I cut the unneeded tab off with *****), GM 1/4" i/d, (3/8" o/d), GM style Wire Loom Routing Clips in for the wiring loom where needed.
Hand tool Tool Pliers Wood Snips

I soldered the connections to the Add-A-Circuit Fuses instead of using the provided crimp connectors and used at least 2 layers of shrink tubing over the soldered connections. I also used 1/4 inch Split-Loom for all the wires run as close as possible to each end of all the wire runs except for a couple short wires between the added relays that are right next to each other and the very short distance between the inner and outer sides of the Wiring Harness Seal where the Wires goes through the firewall on the driver's side.

I also soldered the splice of the + wire between the Fog Lights and kept the long of the two wires, going to the right Fog Light, as a one single piece length all the way from the Relay. I carefully stripped the insulation without cutting the wire for the soldered splice that goes to the left side.

Each Fog Light has it's own ground wire coming from one of the existing body grounds on the inner fender wall inside the engine compartment.

Eventually, I will post some other photos.
 
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