I have 3 issues with my 1999 Yukon SLT, all of which are electronic related.


TYF Newbie
Nov 4, 2021
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So I have a 1999 Yukon SLT I bought used. I'm having 3 electrical problems with it that are most likely not related but I figure I'd pour it all out in case one might cause the other. Let me preface this by saying I am not a mechanic. I'm not even a vehicle hobbyist. It's just my daily driver and I'd like to be able to fix it.

So problem 1: My headlights stay on at all times whenever the truck is running. My headlight switch only turns the running lights and the dash lights on and off. When I turn the switch on at night to see my dash, my back driver side tail light assembly (the entire thing) stops working. If I turn the switch back off all of the lights work fine, but my headlights remain on.

Problem 2: My Heat and air began working intermittently and only on the highest setting. Even then, when it would be very cold or very warm, it would stop working. As I drove for a while, it would randomly start working again. I did a little research and saw that it was most likely the blower motor resistor. I went to O'Reillys this morning and bought a replacement as my air would not blow at all today, and installed it about 2 hours ago. I made sure the harnesses were connected after installation and started my truck up with nothing. When I get moving, air can be felt coming from the vents but it's VERY VERY weak regardless of what setting its on. The people who owner the SUV before me had obviously encountered some issue before because when I took the glovebox off, the mount holding the relay wasn't even bolted in place. I was just laying on top of everything. I watched a how to video from 1aAuto on how to replace the resistor (they showed a '97 Tahoe) and they showed 3 wiring harnesses where I only had 2. I don't know if that's normal or not considering they're different year and models. But this is by far the most important problem that needs addressed. I can live without AC. I need heat in the winter time though.

Problem 3: My driver side power window wont go down at random times. Other times I'll be putting it up and it stops halfway up. I assume this is just a short in the switch, but I figured I'd throw it up here just in case.

I apologize if these issues have been addressed before but I'm at my wits end with this HVAC issue. Any help is much appreciated.


Full Access Member
May 14, 2017
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1) DRL- headlights on when key on. Taillight issue may be ground near bulbs. Test seperate with switch on.
2)Likely the control panel- need a tech2 or vcx nano or comparable scanner to be sure.
3)window track needs grease/ window felt too tight- try some soap on felt to see if it changes/ window motor weak.
Try to narrow your descriptions as you figure out more.


Full Access Member
Dec 21, 2016
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On that blower, does the blower still turn on with High?

Pull the connector from the resistor and there will be four wires. On the connector side, use a multimeter and check for voltage on each wire while changing the blower switch. You should see varying voltage corresponding with the low to medium-high dash setting. Diagram is attached.

If that checks out (you’ll get full battery voltage only on high and that goes through the relay, bypassing the resistor) then I’d swap the relay out since that’s the next thing downstream short of the blower which you know works.

If you get no voltage at the resistor connector (see if it changes by giggling the panel blower knob) then I’d swap the panel blower switch out. They go bad, even brand new ones.

Pull the a/c panel out and the switch is held in by a screw and a few plastic clips. The knob pulls off.

Honestly, though, the panel clips are 95% probably going to break when you do it. They’re probably already broken from the previous owner. It’ll still work and everything, but it wouldn’t hurt to grab a junkyard panel as a spare and just toss it in to see what happens. New ones are (1) expensive and (2) not very reliable at all.



Apr 18, 2021
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I'm late to the party hope you've got it all fixed by now.
That truck has DRL indicated by the green light on the dash, they come on with the truck running, when that is on you won't have taillights just DRL. If he TL goes out possibly something wrong in the TL. They use a junk circuit boar that the bulbs plug into.
Blower problem many times is a melted connector at the back of the blower switch. Many times you can take it apart and clean it and get it to make contact, if not the connector is available in a kit you can find them on ebay.
Pwr. window could be the switch easy to access and test. Usually when the motor goes bad it doesn't stop part way they usually quit when the window is down and it's raining.

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