I was just thinking for customization that is all. If I was GM and I was God in terms of your vehicle, I would select the BCM too. It's better. It's just that I want to tweak some things and I cannot.


(This a random picture from the net. Not mine. Not my couch)

For instance, I put this type of headlamp switch in my van for the foglights that I still have not yet installed. I cannot just hook the one white wire to the BCM as the GM Factory does because I cannot program the BCM. This means I have to do it another way, perhaps with a small arduino board. It's $5 and an extremely simple program. Run an output wire to a relay and done. I was just on this whole gig about keeping my truck looking factory and not cluttering it with after market crap. If I need a switch I generally look to GM to see what they have first. Maybe I shouldn't make things so complicated but I do.

 

Yes you are way too hung up on factory config :P
It's your van now.

Just hook the switch up to a relay and be done with it! (not sure why you need a microcontroller for that?)
Then it's easy to integrate and modify in the future.

You are also contradicting yourself. If you went the BCM route then it's locked in.
You can't have factory behaviour AND modular customization right?

 

Without me going outside in the cold to look, is the fog light switch the bottom half of the dome/dimmer part?

And I'm with Joe on this one. Find the lead that goes to the fog switch, feed it to a relay that takes power from the the low beam headlight bulb. And then, to make it operate like stock, another relay to cut if off when the high beams go on. You won't be able to tell the difference.

 

That might overload the headlamp circuit. I would add either separate small fuse block or inline fuse.

 

Yes. The foglight switch is the bottom half of the dome/dimmer.

All these buttons on all your switches.. they do not carry amperage. Most of the time they do not even carry Postive(+) Voltage. They are simply push buttons connected to your vehicle ground; Negative(-). A momentary push of the button sends a Negative(-) ground to the appropriate connector on the BCM. The BCM reads this as a signal. There is no power involved. The signal received by the BCM is interpreted by the computer software and from there another signal, often a Positive(+) Voltage through another wire, is sent to the appropriate relay. I cannot hook that switch up directly if I wanted to. It is only a momentary push button to switch a microprocessor on or off. That is why I would need the $5 micro-controller. It's all simple once you get your mind around it. In fact, if you could build your own BCM you could do really some cool customization. That would be a lot of work however.

I am good with this stuff. At least the fun of it all. It's just no fun for me when GM ****-blocks us. Which is probably a good thing, who wants to buy a mess programmed by someone else?

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For more advanced stuff, this is an excellent explanation of CANBUS.


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I should clarify the above. Some of your switches are slightly more complicated than simply a Negative(-) ground lead push button switch wired to the BCM as an input signal. Some of the buttons have a Resistor in the line. This Resistor gives a value measured in Ohms. The BCM simply reads the Ohms to know if somebody touched the ankle or the wrist (the truck being a human body). In this manner, using Resistors, multiple buttons can share one wire returning to the BCM. This cuts down wiring choking the spaghetti bowl as well as costs. Copper is expensive which is probably why GM uses exactly the thinnest gauge wire they can get away with on the circuits.
.

 

That dial looks like it can handle the 0.1A or so that a relay needs just fine.

Polarity is irrelevant if you're isolating the switch. The BCM is out of the picture

You absolutely could. If you're really worried about the relay current, then all you need is a single logic level transistor. A microcontroller is like using a sledgehammer to hang picture.

Our vans use surprisingly little of CANBUS compared to most modern vehicles. Luckily, most systems are still pretty old fashioned.


Which vehicle is that dash panel out of?

 

You are all missing the point. That is a momentary push button. I am not going to told it in with my finger just to keep the lights on. Next, what does the size of the dial have to do with anything? Perhaps I should show you how your radio dial is made. No different. I would have to look again, but I believe the only way to use that switch is negative(-) out. There is no putting power to that switch or even drawing power through it. You will mess with all the other lights and the computer if you do that. It just the way it works. It is ingenious really. A BCM allows for multiple control points and behaviours. All a designer has to do is design the form for ergonomics and a programmer decides the behaviour.




Arduino is simple. $5 and simple code. This little guy is all that is needed. It used to be $5 from what I remember anyways. You could probably control a few different GM push buttons with it.

##### CODE ####

If FOGLIGHTS are Off -> When button is pressed -> Turn FOGLIGHTS On

If FOGLIGHTS are On -> When button is pressed -> Turn FOGLIGHTS Off

#### END CODE ####

Done.

 

Ah OK. I overlooked the momentary switch part. Still, the only way you're going to mess with all the other lights and computers is if you connect it to all your other lights and computers. We were suggesting to put it completely separate. But yeah, you would need either a toggle switch or two-transistor latching circuit to control the relay. I still suggest that if you ever hope to finish this project (in addition to your others), then put down the bleeping microchips and whack the $2 switch in your dash somewhere. You can digitize it later when you have nothing else to do.

Either way, we have now completely derailed this poor guys turn signal topic. I'm stopping here and you should start a new topic if you want to kick this can down the road some more.

 

True enough... somehow I figured he solved that, but maybe it was me... maybe I just switched his problem off. I will have to re-read. Incidentally, I did read the BCM can start acting strange if you are not careful about changing values (resistance, capacitance, etc) on it's feeds for input. So one best needs to understand how the GM System works before hacking some customization into their hardware.

 

Hi all. I have a 2004 Chevy Express passenger van. The turn signals have been flashing fast only when it's cold out. Both directions the same. When the vehicle interior temp is warm it works fine. It started doing this last year, but this year its more noticable. im due for inspection. Thoughts?

I find it odd, but I forget how those work. Perhaps temperature would affect it. As for inspection, does the State say how many times a light can flash in a minute? If the truck is warm at inspection time it shouldn't matter.