Does anyone know how the light out indicator system works?
I added a dash cam to a doubled up fuse in the exterior light fuse panel and sometimes the 'Light Out' bulb is illuminated and sometimes not.
I would have thought adding more load to the system would not cause this, apparently not.

 

Apparently there is a min AND a max current sens for the bulb circuit. I thought it would trigger only if the current dropped off from normal too.

 

Are you sure this is the cause of the light illuminating? I would take the circuit out (both the hot and ground) and see if over the course of a couple days/weeks, if it lights again. Might be a coincidence?

 

I have checked all the bulbs and found none out with the bulb out indicator lit.
Where is the gizmo that senses problems?
There was no problem when I added the dash cam, then a few days later it came on, then went of for a while. Now it is back on.
I first thought it was a bulb out, and just a coincidence, apparently not.

 

My tag lights would cause my light out bulb to come even though they were on,I would open and reclosed the hatch the indicator would go out.After cleaning the bulb ho,ders and installing new bulbs problem was solved.

 

Bump, who knows the answer?

 

Dave, can you move the dashcam hot to another fuse in the main underhood fuse/relay box? I am not quite sure if you have a particular reason to use that fuse to piggyback on to. If it is causing the dash light to come on, and you move it to the under-hood box, maybe it'll stop giving you indications?

 

I realize that but I just would like to see the cause of this. The MB forums talk about a 'N' module.

 

In what context?

 

I can't say that I know for certain, but the schematics show that we have an Illumination Control Module located in the fuse box area. It appears to have 21 pins. Does it contain the resistance sensor that you're looking for? I don't know, but guessing yes. Clean and check the related pin(pins)that correspond to the circuit in question?

 

Curiosity drives a lot of 'why', I cannot tell you how many instances of this basic tenant involves my desire to help. In this instance, I don't have an answer. I wish I did, but there are way too many variables to even postulate a concrete theory. Something causing a concern like this, I would just move to another hardpoint. In the back of my mind (like Dave) I would be bothered until either it gets moved far back in my priorities, or I just move on. Electronics are just too 'unpredictable' to troubleshoot because of way too many variable that are unknown or unavailable to duplicate. As an example, my attempts to troubleshoot systemic A/C control head (re-occurring) issues. I have been unable to acquire a defective head donation from members (even if I reimbursed for low bulk cheapest shipping). Not to digress, just to point out that any situation presented for analysis, there has to be some give and take involved. I applaud 180's questioning 'why' but my experiences in these areas just cannot explain his specific situation. In my example, I have centered on a specific clue (only a start) for the A/C head issue but have (since asking for a donated head unit) only had offers to buy a defective head (as a cost share to help a member reduce his/her repair bill?) or no offer at all. This kind of response makes me feel like any contribution offered by members isn't appreciated by a lot of members. Sad to say that but regardless, I will (like many others) continue to help those who appreciates the free information available to all. On one more note, I have the feeling a few 'new' members, are actually reselling crossfires, and are stuck with something wrong with it and are wishing to fix it for the next owner. I actually applaud these folks trying to sell a car that's fixed but have a funny feeling about how they go about the way they are getting it fixed. either way, I hope whomever buys the car gets it fixed before they pay the monies asked. In the end, those who try to help do so without any hidden agenda.

 

The illumination control module is the light switch on the dash and the fuse panel on the end of the dash is a part of it. Inside the ICM there are all sorts of goodies, maybe whatever senses the load is in there.

 

Guessing there is both low/no current sense for an open bulb and a high/over-current sense for a shorted condition built into the ICM. Otherwise more current should not be an issue when the additional circuit was added. The over current is the rarer monitoring situation.

You are he super secret document guy, can you get access to factory schematics of internals?

 

The 'N' module senses the bulb out condition.
From a MB site
'That was the cheap one. Far more expensive is replacement of the bulb warning module (it is not a relay). It is the largest item in the fuse box and is part number 126 542 01 32. Most if not all, W126 and W124 cars and perhaps others, use this same module. See if you can borrow one just to try it before you spend $$$ on a replacement. MSRP is $210. They are available aftermarket new and rebuilt for less.'

 

Wow, they used to do that with relays? To monitor bulb current it's simple ohms law, voltage drop across a known resistance when the bulb is good and when the voltage goes away light a light on the dash is the theory but how MB accomplished it in the Crossfire, Hmmm....

Now to monitor excess current you gotta add some stuff...

From the picture below, the in and out would be to and from the bulb circuit on the car. The Rsens is the known value for the known bulb. The analog out would be to the cars computer programmed to monitor a range of X, outside range X would light the bulb out indicator. Yes, you can deduce from this if you wanted a ton of work to do you could change the value of Rsens for the LED's installed on your car and successfully monitor non CANbus compliant LED's. In doing so you would be locked in to the one LED brand and style of course. CANbus compliant LED's have a parallel resister in them to fool the car into thinking the correct bulb is out there by drawing the same amount of current as an incandescent bulb.


http://openenergymonitor.org/emon/si...rrentSense.jpg

 

The quote says 'it is not a relay', there are relays in that area is what I understand from that statement.
The system can detect at least a 3W drop.

 

Are you adding 3W with your camera? Just a theory, might the circuit also detect a 3W increase? I times E = power so current of the camera times voltage will equal watts. So 13.8 times any more current than .22 would be a 3w change. Does the camera draw more than 220 milliamps?

 

Just looking at the exterior of a few of these (your part number 126 542 01 32), I found this ( 126 542 01 32 - Lamp Control Module - Album on Imgur ). Other than that I have no idea how it (the circuit) is designed/works, it looks wildly complicated and not something I would want to 'reverse engineer.