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Okay, so this represents a ton of firsts for me: First time posting in a forum, first time owning a truck (or any vehicle for that matter), and the first time working on a vehicle, so I humbly ask for your patience and thank you in advance. Please understand that my knowledge of vehicle mechanics is fairly limited, but I do a little better with electronics.

 

I recently purchased a 1989 GMC 2500 for relatively cheap, and was assured that it was very mechanically sound, which it is, I think. I didn't realize that there were a lot of non-mechanical issues with it, even through a test drive. One such issue is with the speedometer. Usually, when it is colder outside, or I am making the first trip of the day, the speedometer works perfect. After that, though, the speedometer doesn't work, and I have to use the GPS on my phone. I have no idea where to start, other than pulling the dash apart, but then I will just get a stupid look on my face and not know what the crap is what. I did check all the fuses, and only one was blown, but more on that later.

 

Another issue is with the odometer. It claims just under 104k on it, which is amazing, until you realize that it is horribly inaccurate. Whenever the speedometer is not working, the odometer is not turning, so I assume that they are linked somehow. However, when the speedometer is working, only the tenth of a mile wheel spins, and nothing clicks over. Both of these can wait, however, until after I get the safety inspection done that is required yearly by the great state of Utah. Other issues are a little more pressing, such as...

 

Headlamps. How do I properly aim them? I did buy a Haynes repair manual from O'Riley Auto Parts, but it wasn't as specific as I would like. It listed two different kinds of headlights, and explained how to aim them, but what is on my truck looks like what both were described as. Another pressing issue is the tail lights. When the head lights are on, there is supposed to be a dim light in the tail lights, right? On the right side tail light, there is. On the left side, there isn't. On top of that, neither of the back up lights nor the license plate lights work. In addition to all this, the hazard lights don't work. Of course, it would help to check the hazard lights if I knew where the button to turn them on and off was located.

 

Now to the blown fuse. This one boggles me. The fuse was for the park lights, also required by law. It is a 25 amp fuse, which is easy enough to replace. However, when I replace it, no matter any thing else in the vehicle, the park lights come on, along with the head lights, and there is nothing I can do to turn them off except for removing the fuse. The park lights come on without the button even being used.

 

I know that this seems like a lot of questions to ask all in one post, and I'm sure that they are covered individually somewhere on the internet, but I really don't know if any of these problems are causing other problems to happen. I really need this truck to pass inspection, and I would really like to do the work myself, as I did get the truck so that I could learn this kind of stuff. And in case you are wondering how in the world did the previous owner get it to pass inspection, he had it registered in a county that doesn't require safety and emission checks. I really wish that I could do that, but I don't have a relative living in one of those counties.

 

Anyway, I do appreciate any and all help that y'all can give. Like I said, I know very little about auto mechanics, but I am trying to learn. Thank you again.

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first of all, congrats on the new truck and welcome to the forums. Are you anywhere near Layton? I know a great shop down in that area that I trust. Don't get too overwhelmed with what you have in front of you.

 

For the lighting issue, I suspect a bad switch. Should be able to find one relativly cheap be it at a junk yard or online at ebay. You'll want to inspect the wiring very closely, going into the switch, and going into the various lamps. With you being in Salt Lake, the salt and sand used on the roads will have taken it's toll on the truck. Can you get us some shots of the truck, inside, outside, front, side, and rear? What size engine do you have? Manual tranny or automatic? Shots of the istrument cluster as well. Is this a 4X4? Get us a shot of the engine compartment too. As for the hazzard lights, I am pretty sure that generation still had that little black knob down on the right side of the steering column not too far from the ignition switch. You push the button in to activate the hazzards, then pull the thing around the button out to de-activate. Any owners manual for the thing? Go ahead and take off the housings of the taillights and inspect the wiring, go ahead and replace the bulbs in the taillights and use what is called for. Replace the bulbs in the license plate lights as well. Check under the bumper as the wiring for those license plate lights may have been cut or corroded. Depending on what front end you have, I'll give you a hand with that when I see the photos. We'll get you sqaured away, my friend. The great thing about these older trucks is that they are super easy to work on.

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  • 4 weeks later...

Sorry for the long delayed reply. I wrote the first post with the hope that I would get some answers flowing while I was out hunting for a few weeks, then forgot about this until just barely.

 

Colossus does bring up a good point: I need to say more about my truck. It is a 1989 GMC Sierra 2500 4x4, 5.7 Liter 350 CI engine V8 automatic. I do actually live very close to Layton, in a little town called Kaysville. So, Colossus, if you could shoot me the name of your mechanic you trust, I might just have to look into it. I will upload some pictures of the truck as soon as I figure out how. I keep getting an error message that I can't use that extension on this forum, even though I have tried .jpg and .gif.

 

I was in the middle of installing an airhorn when I remembered that I had posted here and needed to reply. The original horn on the truck does not currently work, and I need one to comply with law. I've always wanted an airhorn, and I can't find the wiring for the horn on any schematic, so I figured now is as good a time as any to get a big horn.

 

I did find the hazard light switch on the steering column. The knob is missing. Then, me not really knowing what I was doing at the time, pushed the button and couldn't get the button to release. I ended up having to drive down to O'Reilly Auto Parts to borrow a steering wheel puller, remove my steering wheel, and push the post from the backside. There is a hole in the post that looks like a knob could screw into, but after looking at a new one, I can tell that the hole is really stripped out. Instead of attempting to replace the knob, I have opted to go for a toggle switch installed in the dash. I just don't know which wire I need to splice into. I believe it is the purple one, the wiring schematic that I have lists purple as "Flasher out", however, it also has "Hazard Power", "Turn Power", and "Ground". I thought it would be fairly straight forward, but I quickly found out that I get a signal out of about 5 wires instead of just one or two.

 

I also crawled underneath the back end of my truck to look at the license plate lights, and found that the wire had indeed been cut. I'm not sure why, but it is, and I don't know where the wire is supposed to go, either. I am guessing into the park lamp circuit, but I do not know where at, if that makes sense.

 

Other than these few things, I haven't really had much time else to work on my truck. I thank you again in advance!

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