Wiring Diagrams - What Gives?

Hi- the more and more R/S I install the more I see that the typical wiring chart always says to find parking lights, brake input, door locks, trunk releases, etc all at their primary switche locations.  But as I go - I find it much easier to pull a wiring schematic out of the BCM and determine inputs and outputs and wire all that I can out front of the BCM.. Why would one want to struggle to tear open kick panels, dash board light switches, trunk releases etc when most times all these can be BCM connections- most generally on the same color wire as described in the wiring charts.  Man this speeds me up considerably- If I don't have to pull down  a panel to access a really hard brake switch, and the BCM is under the passenger side glove box- I can actually solder while sitting in the seat!!  I am just curious as to why all the charts act like they don't know that most all wires begin or end at the BCM.  

 I just did an '03 Malibu last night and really struggled to hook up the horn chirp wire under the stupid steering wheel plastic cover-- what a pain-- when I got to work< I saw that I could have used pin a4 on connector 1 of the BCM that is in parrallel with the horn button- since the BCM also has a horn relay control (-) capability.  What a waste of time- I followed the charts and it could have saved me 20 minutes to have researched the BCM connector schematics first....... Any thoughts?

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Brcidd - Engineer That Does Remote Starter Installs on the side.

Weird! The horn wire at the steering column on the 03 Malibu only took me a few minutes to grab. But I do know what you are talking about. I think I just have good wire databases that often have such information, including pictures.

With more experience though the connections are so easy to grab that looking up the wires in a BCMw diagram might start to slow you down even if you have access to all of them. I say this coming from the experience that my information does a fairly good job at locating the wires in easier locations.

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J Rilla

Owner/Installer

Bow down to BCMs...

I like when they say...

blue (+) kick panel...

Only the kickpanel is covered in plugs and wires all over.....how about a little more indepth description like low in kick panel in harness that goes to back of car.....etc..etc..

If any of you guys have access to wiremagic/autoland  that stuff is awesome...they have started putting pictures of the actual wire with a little arrow and a description box.  pretty sweet..    Far better that techsoft from DEI...

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"I just did an '03 Malibu last night and really struggled to hook up the horn chirp wire under the stupid steering wheel plastic cover"

You could've saved yourself that 20 minutes and grabbed it near the steering column. No reason to take the shroud apart.

As far the BCM question, it really comes down to preference. I would rather take a kick panel apart then run wires to the passenger side of the vehicle behind the glovebox. Generally the further around the car you go the more time you take. BCMS aren't always in the drivers underdash area so it doesn't make sense to run wires to the BCM in all cases.

Another thing is that most installers don't have access to factory manuals with BCM printouts. So listing "Park Lights: white (-) @ pin 200 of 3 million @ BCM" isn't much help. Especially when there's probably 20 other white wires in there and the plug is too hard to access to count the pins. That takes too much time when I could pop the headlight switch and only have 1 or 2 white wires that could possibly be it.

Finally not all of use rely on wiring charts to complete installs we may reference them for one or two wires if available, but everything else is grabbed at the logical spot.

Anyway there's some different views on it. Don't get me wrong put a BCM in an easy to work spot and I will use it for everything it's worth.. Later,

Mike

Mike

I did a 04 Impala and when I had to hook wire to the bcm I was upside down on the floor board.Some are easy  some are not.

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BigDog

I think the real problem is that to list the BCM wires you need the tech manual for every car on the road. While I don't know how DEI, for example, acquires their info but I doubt they have the service manual for every car on the road. The cost would enormous. Just the electrical manual for my wifes RX300 is 125.00USD. If you have the time and access to the ECwould expect to find it. ECUU/BCM you could test the wires and just be patient but even some cars have the BCM/ECU in the engine compartment not in the passenger compartment. Sounds like DEI may not be the "best" place to get wire info. The best place to get info is on this site. Get the shortcuts from the pro's here that have found wires in weird places rather than where the diagram suggests. For example on a diagram I saw for a lexus is stated the tach wire was in the engine bay as you would expect but from a tip I found it right next to the fuse panel in plain sight! What a freeking time saver! 

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Jeff
Always Verify Wire information before Connecting! Just a Darn Good DIY'R

Personally, I think getting lots of info. from different wire diagram is very important if you want to save time. I can tell you from experience that there were so many instances where I was able to find the wire but no way on hell I was able to get to it. The only way of getting the job done was to go to a different wire info. and through someone with lots of experience.    

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Be careful whose advice you buy, but be patient with those who supply it.

Check your local library. I have access to a limited amount of book form shop manuals that I can get wiring diagrams from and I can also log onto ALLDATA's website and have access to just about any car I want. When I know the car has a BCM, I just check out Alldata's site and print out the connector pinouts for that particular car. It tells me what pin # and color of wire...too easy!