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Discussion Starter · #1 ·
Hey all I hope all is well. I need help with a fuse issue, it started as diagnosing my 4x4 and landed me here.

I have a 2003 gmc Sonoma ZR2 4.3L

under my hood the fuse box has multiple fuses that are not getting power. I changed the fuses and nothing changed then I probed the actual fuse slots with a test light and both sides of the fuse contacts gave me nothing.

the affected fuses are Hvac, Oxysen, ATC and TBC ( his would explain part of my 4x4 issue )

now My two other fuses Trchmsl and Vechmsl, when I probe these the test light comes on very dim and it triggers my brake lights to come on.

im not very good with wiring as is so I don’t really know how to tackle this. Any pointers is greatly appreciated. Thank you all in advance
 

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That's an odd assortment of fuses/circuits to be completely dead, power distribution diagrams don't show any common path between those circuits you listed.
It may be worth removing the fuse box and taking a look underneath to see if something is wrong. Maybe a rodent hung out for a while or maybe corrosion took hold and ate away at terminals in the box.

The Trchmsl fuse is for trailer wiring and the Vechmsl fuse is for stuff like the High Mount brake light, cancel signal to cruise control etc. Both of these fuses only get power when the brake switch is depressed.

Your test light was allowing enough current to pass through it to power the brake lights when you probed those fuses.
 

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It's not often that there is a problem with the fuse box, but........it is possible. It wouldn't hurt to check the power leads that feed the fuse box. There was recently another member that was having issues similar to the ones you are describing, and it did indeed turn out to be the fuse box. I've included a link to that thread in case it may give you some pointers: Fuse box for 1998 2.2 Please keep us posted on your progress and outcome.
 

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All those fuses (fuses are Hvac, Oxygen, ATC, and TBC) without any power suggests a serious large-scale issue. Does the vehicle run? I would start by checking the battery and associated connections. Ensure that vehicle grounding is working as well. If that all checks out, then look at specific issues with the fuse box.....
 

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Discussion Starter · #5 ·
All those fuses (fuses are Hvac, Oxygen, ATC, and TBC) without any power suggests a serious large-scale issue. Does the vehicle run? I would start by checking the battery and associated connections. Ensure that vehicle grounding is working as well. If that all checks out, then look at specific issues with the fuse box.....
That's an odd assortment of fuses/circuits to be completely dead, power distribution diagrams don't show any common path between those circuits you listed.
It may be worth removing the fuse box and taking a look underneath to see if something is wrong. Maybe a rodent hung out for a while or maybe corrosion took hold and ate away at terminals in the box.

The Trchmsl fuse is for trailer wiring and the Vechmsl fuse is for stuff like the High Mount brake light, cancel signal to cruise control etc. Both of these fuses only get power when the brake switch is depressed.

Your test light was allowing enough current to pass through it to power the brake lights when you probed those fuses.

Yes the truck does run it runs great actually if I’m being honest , I’m a little nervous to pull the fuse box off because I don’t want to mix any wiring up ahaha but I guess it will have to be done ! Thank you for the response ! I will keep you all updated on how it goes
 

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Discussion Starter · #6 ·
It's not often that there is a problem with the fuse box, but........it is possible. It wouldn't hurt to check the power leads that feed the fuse box. There was recently another member that was having issues similar to the ones you are describing, and it did indeed turn out to be the fuse box. I've included a link to that thread in case it may give you some pointers: Fuse box for 1998 2.2 Please keep us posted on your progress and outcome.
Thank you for the link I will definitely check that out and I will be sure to keep this updated on what I find !
 

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Yes the truck does run it runs great actually if I’m being honest , I’m a little nervous to pull the fuse box off because I don’t want to mix any wiring up ahaha but I guess it will have to be done ! Thank you for the response ! I will keep you all updated on how it goes
Pulling the fuse box is pretty straightforward, and it's pretty hard to screw it up as all of the harnesses only go in one way. Just remember to disconnect the power (battery) first!
 

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Discussion Starter · #8 ·
Pulling the fuse box is pretty straightforward, and it's pretty hard to screw it up as all of the harnesses only go in one way. Just remember to disconnect the power (battery) first!
That's an odd assortment of fuses/circuits to be completely dead, power distribution diagrams don't show any common path between those circuits you listed.
It may be worth removing the fuse box and taking a look underneath to see if something is wrong. Maybe a rodent hung out for a while or maybe corrosion took hold and ate away at terminals in the box.

The Trchmsl fuse is for trailer wiring and the Vechmsl fuse is for stuff like the High Mount brake light, cancel signal to cruise control etc. Both of these fuses only get power when the brake switch is depressed.

Your test light was allowing enough current to pass through it to power the brake lights when you probed those fuses.
All those fuses (fuses are Hvac, Oxygen, ATC, and TBC) without any power suggests a serious large-scale issue. Does the vehicle run? I would start by checking the battery and associated connections. Ensure that vehicle grounding is working as well. If that all checks out, then look at specific issues with the fuse box.....
Hey all so I got a chance to pull the fuse box off and found 3 pins that have a little bit of corrosion as well as one of the wires , I’ll attach some photos. I’m assuming my next step is to go to the wreck yard and find a fuse box my only concern is that wire, should I be cutting the wires off the other truck and splicing them on to my truck or ? Or is it possible to clean my fuse box up and re use it. Thank you again for all your help
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Based on what you have provided, I would try cleaning up the existing fuse box first. Remove from the truck and clean all the debris out. Next use some electrical contact cleaner on all the connections. Electric motor cleaner is available everywhere. My favorite is DeoxIT, since it not only cleans but keeps corrosion off. But that's not really required at this point. Any electric motor cleaner will do. Then re-assemble and test. You can always buy another unit if needed, but what you have might just work if the corrosion is removed.
 

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Discussion Starter · #10 ·
Based on what you have provided, I would try cleaning up the existing fuse box first. Remove from the truck and clean all the debris out. Next use some electrical contact cleaner on all the connections. Electric motor cleaner is available everywhere. My favorite is DeoxIT, since it not only cleans but keeps corrosion off. But that's not really required at this point. Any electric motor cleaner will do. Then re-assemble and test. You can always buy another unit if needed, but what you have might just work if the corrosion is removed.
Ok definitely I will go grab some cleaner after work today and clean this all up and test. Fingers crossed I really hope this works. I will be back With an update As soon as I have one, thank you again
 

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Based on your photos, I'd be inclined to seek out a replacement fuse box. It could be labor intensive to clean up the spade terminals (small brass wire brush & contract cleaner), and that doesn't include the condition of the matrix of conductors (below the terminals - see photo in post #18 of the link I posted previously), which may or may not be compromised. A good thorough cleaning may, or may not resolve any continuity issues.

And, the 2 red wires' corrosion needs attention. You may be fortunate that it is confined to just the terminal ends, and a robust cleaning may suffice. But it is entirely possible that it has extended back 'up' the wires (inside the insulation jacket) away from the ends. I'd make a small "inspection slot" through the insulation about an inch or so back from the to check that (and maybe another one further away if warranted to determine the extent). edit: If the wire is OK and usable, be sure to repair the insulation to recover & protect the wire.

I don't know if the blue plug assembly is serviceable (i.e. can be disassembled) to properly clean up the ends of the wires' connectors, and if not, then you may well consider splicing on a new (salvaged) connector. If that is the case, be sure to get an ample length of the cables so you can position the splice in an accessible place. I'd use a shielded 2 conductor terminal block to join the 4 ends of the wires at the splice, and make sure that it is properly sized for the wires, voltage, and load (amps) to be carried.

Please keep posting with what you discover and how things get resolved. And, FWIW, besides a salvage yard, you may try Craigslist for parts, as often private parties are parting out a vehicle, and can be very cost effective.
 

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ok- quick and easy for the fuse box spades- fingernail emery boards- bright and shiney is your friend. As for the plugs- disassemble w hat your can and remove the green corrosion.If you have to split the casing back to get beyond the green- look to see if you can remove the plug first!you might get by with just cleaning the spades as you have power in the box at this time.
 

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ok- quick and easy for the fuse box spades- fingernail emery boards- bright and shiney is your friend. As for the plugs- disassemble w hat your can and remove the green corrosion.If you have to split the casing back to get beyond the green- look to see if you can remove the plug first!you might get by with just cleaning the spades as you have power in the box at this time.
And, if you do get power to the box, be sure to check for power at all of the contact points within the box. A fingernail board will work, but personally, I'd use something with a finer grit, and you may need something else to get down to the bottom of the spades.
 

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Discussion Starter · #14 · (Edited)
And, if you do get power to the box, be sure to check for power at all of the contact points within the box. A fingernail board will work, but personally, I'd use something with a finer grit, and you may need something else to get down to the bottom of the spades.
ok- quick and easy for the fuse box spades- fingernail emery boards- bright and shiney is your friend. As for the plugs- disassemble w hat your can and remove the green corrosion.If you have to split the casing back to get beyond the green- look to see if you can remove the plug first!you might get by with just cleaning the spades as you have power in the box at this time.
Based on what you have provided, I would try cleaning up the existing fuse box first. Remove from the truck and clean all the debris out. Next use some electrical contact cleaner on all the connections. Electric motor cleaner is available everywhere. My favorite is DeoxIT, since it not only cleans but keeps corrosion off. But that's not really required at this point. Any electric motor cleaner will do. Then re-assemble and test. You can always buy another unit if needed, but what you have might just work if the corrosion is removed.
So I cleaned up the fuse box and wires really good and it didn’t change anything. so I took a trip to the wreck yard and found a fuse box in great condition gave it a quick clean up and got a new plug for the one that was corroded. Put everything back together and still no power to those fuses.
now I did notice something very weird after cleaning up the old fuse box. The TBC fuse witch wasn’t getting power at all before was now getting power at the actual slot but not when the fuse was in the top test spot showed no power so my first thought ok bad fuse. I replaced it with a new one and still no power at the top of the fuse, so I put the fuse in a known working fuse slot and it worked fine so I’m confused as to why the power isn’t Carrying through that spot and if that could be causing the other fuses not to work. I’ve been trying to find a wiring diagram and bought a service manual for my truck to find out the exact wiring for those fuses and have came up empty. I really don’t Know what to do at this point.

It’s just weird because everything works tuck starts and runs great, no engine codes just those fuses having no power.

my understanding of a fuse box and correct me if I’m wrong because I probably am ahaha but the fuse box gets power from the battery witch goes through the fuses that are being used and sends power to everything. So I’m just at a loss of why these fuses wouldn’t be getting power when everything else is
 

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It gets some of it's power from the battery. For anything that is always hot. Like brake lights.
Things that are only powered when the key is on get power from the ignition switch.
Since you tried a different fuse box and got the same results you have a wiring problem. Some thing is broken or burned thru. I'd start by probing any large wire entering the fuse box that is red. They should have B+ volts at all times. Pink will only have voltage when the key is on.
Have you checked all 6 of larger fuses to see that they have power to them and tested all those fuses with a DVOM?
 

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Discussion Starter · #16 · (Edited)
It gets some of it's power from the battery. For anything that is always hot. Like brake lights.
Things that are only powered when the key is on get power from the ignition switch.
Since you tried a different fuse box and got the same results you have a wiring problem. Some thing is broken or burned thru. I'd start by probing any large wire entering the fuse box that is red. They should have B+ volts at all times. Pink will only have voltage when the key is on.
Have you checked all 6 of larger fuses to see that they have power to them and tested all those fuses with a DVOM?
I’ve used my test light on the larger fuses but that’s it I don’t have a DVOM at the moment but I will take a trip to the store and pick one up! When you say it should have B+ volts what does that mean exactly? The volt meter will show Battery voltage ( 12 ) and then + whatever volts are coming from that wire ? . I’m sorry I’m not super knowledgeable on all of this stuff just trying to learn as I go. And when I probe the larger wires should I be sticking the end of the DVOM straight into the wire through the coating ? , thank all you guys for all your help.
 

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B+ means what ever the positive terminal of the battery has for voltage at the time of the test.
Fully charged new battery is around 12.5. One a year old might be 11.6 or so.
It simply means that it doesn't necessarily need to be 12.00 V.
 
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