"Does the display on the heating-A/C control unit turn off when the ignition is turned off."

No, it also stays on. If you hit the power switch on the HVAC unit on the dash, it goes on, whether the key is in the ignition or not. If I'm driving the truck, and park it in my driveway and take out the key, it stays on, unless you remember to manually hit the power button.

"Are you dead-certain the sensor fan is running with the ignition off?"

Absolutely certain. I unplugged it, cleaned it and reinstalled it. It runs, key in the ignition or not.

"Was your truck converted from air springs to coils?"

No, the truck never had the air ride system.

It seems as though anything on that system is not being powered down when I take out the key.

Thanks again, for everyone's input.

 

Possibly there's something amiss with your ignition key circuits? Looks like the common factor is fuse 31, which is supposed to be switched by the key.
Although I don't know why everything else that's key-switched wouldn't also be affected.

 

Yes it does sound like ign system and the switch is about only thing that would cause that.
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Can the ignition switch actually leave just one circuit on?


And if so, I assume I need to replace the ignition switch?

 

I looked at the diagrams again.

Ign switch would not leave just the HVAC circuit non-powered but the other circuits being powered as well don't have a small fan in a sensor to notice running and cause some if not most of the drain. That switch contact appears to also be powering fuse 30 for CC and mirrors. Check to see if you can adjust your mirrors with the switch off.
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You are correct sir.


Mirrors still have power. Also, the CC switch lights up when depressed. Is this one particular leg of the ignition switch mechanism?


Thanks again, you guys are amazing.

 

Yup per the diagram 2A. No guarantees but I'd be looking towards the switch. Also some chance of wiring is rubbed raw at switch plug or on way to/from pax fuse box.
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I would think that if the wiring were compromised, it would short. This just stays on. The actual mechanical ignition tumbler works fine. Key goes in, turns, car starts, it turns fine to shut it off. The only issue is that the one leg appears to not shut off.


Looking at pictures it appears as though I should be looking at replacing the round black plastic main switch that connects to the end of the metal tumbler housing, and pigtails under the dash.

 

These trucks have knows issues with other components in that area getting dirty and malfunctioning... such as the wiper control and headlight wands. You might try opening it up and cleaning it. A chunk of debris or corrosion on a contactor could leave the circuit on.

 

Toss that in as a slight possibility. If you look at the diagram if the 2A output wire and the power into ign switch were to rub enough to wear through insulation and touched it would do the same, constantly power the fuses in question. That would be two wires shorted together. Unlike a short to ground it wouldn't blow a fuse.


That's a possibility as well. GS needs to decide if he wants to take the time to tear things apart to check and possible find nothing obvious and/or have a switch in hand to swap in once things are apart. More time than money or more money than time?
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