I hate to bother people with this, and I wouldn't normally ask, but I've pored over all my technical documentation and can't find this anywhere (some of it only covers up up to 2009). Maybe somebody with a data subscription can help me please. (cough... @jack62 ..cough)
I'm trying to find out where a ignition key switch signal leads to. I'm interested in position I - accessory ( Not II-run or III-crank).
I suspect it leads to the BCM, and the BCM recognizes that accessory mode was requested, and it energizes various circuits. But it would be really helpful to have a schematic to see the path it takes, the circuit number, wire color, routing location, connector pin numbers etc. I'm interested in tapping it off and using it as a control signal to switch on some add-ons.
I seem to be missing a general power distribution schematic as well.
2013 GMC Savana 5.3L
VIN 1GKS8BF47D1128683
Here's what I was able to find.
On the website, the12volt.com,
https://www.the12volt.com/installbay/forum_posts.asp?tid=141115
On the partial ignition switch wiring diagram you posted it shows Ignition Start/On voltage coming out of the ignition switch on pin2 through the Circuit #3 Pink wire to the BCM X1 connector, Pin 14 and that matches up with what it says 3 lines above the highlighted text (so that's promising).
On https://www.gmupfitter.com/light-duty-vehicles/light-duty-2013/ under "full size vans" there's the 2013 G/H Full Size Van electrical manual.
On the Manual page C-1 (pdf page 104) it has the pinout of the BCM X1 connector.
That pinout matches your partial wiring diagram where Ignition On comes out of the switch on a Pink wire, circuit 3, and goes to the X1 connector on Pin 14.
And going back to what it says on the12volt.com, Ignition Switch Accessory is coming into the BCM X1 connector from the Ignition Switch on a Brown wire to Pin 21 (Circuit 4).
The Electrical Manual also shows the pinout of the Steering Column Harness connector which shows the Circuit 4 Brown wire there. Pages C-36 through C-38.
I looked around for the ignition switch pinout but I couldn't find it anywhere.
So maybe do a voltage test on that Brown wire from the ignition switch at the most convenient location and see if that's the one you're looking for.
Well I tried and I tried and I tried but my all data system for that vehicle is squirrely. It goes round and round and when I get to that area and click on the harness it just goes back to the general overview where you started from. I get all the way down to the steering column wiring and then it just goes back to the beginning when I click on diagrams. Really all data systems has so many flaws these days.
Here's what I was able to find.
That really helps. I'm going to investigate that brown wire.
I use the upfitter manuals often. They have been invaluable, but sometimes they're incomplete or even misleading. (like calling everything "Ignition Voltage")
So what's your favourite way to tap into existing wiring? I was thinking about using wire nuts or terminal strip.
Thank you, Jack. I appreciate it.
I don't do much of that but I've seen it done on aftermarket alarm and remote installs and I prefer when they don't cut any of the existing wiring whenever possible
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If you have to use a control signal voltage to energize the circuit for your "add-ons" in Key position Accessory only, see if you have the room to solder the wiring connection. Like this:
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If you don't have the access room to solder the wiring then maybe use a T-connector like this one
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The only other thing is to be mindful of that existing wire's gauge and not to overload it