I really need some help guys, if anyone has any knowledge of the HVAC wiring in these trucks. just to throw it out there, my number is seven 6 oh, 405-3016. Here's what happened........................I really have no idea what happened, to be honest...one minute it was working, the next it wasnt. I lost the lighting in the panel, and the blower motor quit working. I've pulled the motor, and tested it on the bench, and it spins perfectly. I checked the resistor (visually) and it seemed fine, but to double check, I overnighted a new one from Rock Auto. This is where I can't figure out what's going on. I have 12v to the fan when the truck is on-it should be spinning, but it's not. Also, the lighting in the hvac panel went screwy all of a sudden...now, with the truck running, and the lights off, when I turn the top knob (It's a 2000 model interior) to any one of the running positions, the panel lights up. As soon as I turn on the lights, the panel goes dark. The problem I'm running into is I can't find a wiring diagram for the back of the panel to save my life, and I don't know what wires are supposed to have power/when. I'm in the middle of packing up the house, as I'm moving to Indiana in a week, and I need to have the HVAC working. The heat and cold works, blend door is good, and the vacuum still switches it to the expected positions-dash, defrost, etc. The biggest problem is that the fan won't come on. I'm almost at the point of cutting the wires to the fan, and running a toggle switch to it, so I can at least turn it on when I need to, even though it would only come on on high all the time-but I'm afraid of burning up the fan motor. If anyone has any ideas, please call me-I truly don't care what time of the day/night it is, as I HAVE to have this fixed before I hit the cold weather. I'm not that worried about being warm, but if I can't defrost my windshield, I'm screwed. I've been messing all day, and I can't figure out what voltages and what grounds are supposed to be where on the back of the panel. I really need help guys. I almost posted this in the 911 section, but considering I'm not actually on the road, I felt I couldn't justify it yet.

You say you have 12 volts to the fan but do you have a ground? Also if the resistor goes bad, it will only work on high speed.

I do have a ground the orange wire coming into the fan is my ground there's a black wire with a brown stripe that is coming off of the back of my controls. There's a black wire with an orange stripe going intoy controls thats a ground. I noticed that when my fan switch is maxed out, the black wire w/ orange stripe and the black wire with the brown stripe on my controls are connected-ie shorted out on the panel. Problem is something is shorting out the entire thing...is the black and orange wire not supposed to be a ground?

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If anyone would be willing to call me if they've got any experience, I'd appreciate it...I barely get enough signal to get online outside, so I tend to miss posts or takes me 30 minutes to reply...

You say you have 12 volts to the fan but do you have a ground? Also if the resistor goes bad, it will only work on high speed.

Bingo... Most of the circuits in these truck have constant power +12V from PDC but the controls tend to switch the grounds off and on. So with the panel lighting and the controls there grounds should got to either a center of the dash ground lug or over to the driver side kick panel. I know the image is a bit small but you get the idea...

Hey all, finally figured it out! I'm glad you guys mentioned grounds, because that's what it ended up being. The goofy thing was, well, I'll get to that. So, testing at the back of the HVAC control panel, the line of wires starting at the top and going down:1. (thin orange) illumination2. (dark green) AC settings only (Max, AC, Dash/floor, defrost/floor, defrost)3. (light green) low fan setting4. (can't remember) next fan setting5.( think it was purple) next fan setting6. (black w/brn stripe) Max fan7. (black w/orange stripe) ground.At the fan, it was an orange wire, which was my 12V positive, and the black w/brn stripe wire. What happens inside the switch is that as the fan adjustment turns, it grounds out each setting of the fan respectively, allowing current to flow, thus engaging the various speeds of the fan. (I just figured this out tonight, in depth...) I did notice that with the illumination wire connected, as well as the ground (black w/orange stripe) the lights would activate correctly, after a few minutes of messing around. Then, I took the wires out of the connector, and started applying them one at a time. However, once I applied the max fan wire, it would short out, and the panel would go dark. What threw me off the longest was the fact that as I was ohm checking the wires, my ground wire ohm'd out as a short to ground every time...but it must have been a bad ground. I was testing it to the metal on the truck, so it appeared to be a good ground every time I ohm tested it. The reason I finally figured it out, was that I went to the fan, tested the voltage coming into it, which was good, and then reached over to the wires for the HVAC controls. I then touched the Max Fan wire (black w/brn stripe) to the ground, and nothing would happen. So, I disconnected the fan, and jumped it off of the power wire, and ran a temp ground to the dash with some loose wire. Fan kicked on immediately. Once I discovered this, I went and attached a longer section of wire to the Max Fan wire at the HVAC control panel. After applying power, (turning the key to the run position) I then touched the loose end to ground-fan started immediately. I knew I had a bad ground. Ran a new ground, and called it good. (Remember, my harness is a hack job of a 96 12V, 2000 1/2 ton gasser, and 98 12v. There's not a lot of wiring that is "Factory" any more)Like I said before though, the thing that threw me off for hours was the fact that the preexisting ground continued to test out good, every time I checked and rechecked it...so I kept going in other directions. Whatever it tested at, apparently wasn't good enough to make the connection. Control lighting is good, all the fan speeds work, the temp works, and all positions work...I'm good to drive, especially if I need to use the defrost! Thanks again for the replies, and like I said-they got me in the right direction!

Hey Dennhop, glad you got it figured out. Not sure what part of Indiana your moving to but the further north you go the more your going to need it, especially with the humidity they tend to see. Good luck with your move and be safeJR

One other thing is that if your vents stop working (will not change positions) then make sure that your vacuum hoses in the engine compartment are good. I found two junctions bad and leaking vacuum. Replaced them and the vents and A/C/heating work fine now.