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Hey guys.
Edited to add:
1983 GMC Sierra Classic, 305 V8, Quadrajet Carb, H Vin Engine.
C1500 1/2 ton, 2RWD, 5.0LHere again with my truck. Been struggling with this for a while.
The issue: There is an inline fuse (where a fuseable link previously was) that keeps blowing.
The History:
1)The first time I had this issue, the fuseable link had fried, so I had it taken to my mechanic. He concluded that there was a live ground somewhere in the system with the ignition off, and key removed, by touching the fuseable link ends together, and it would burn and spark when touched together (similar to what a pair of jumper cables would spark when touched together when on a good battery and you accidentally touch the ends). Through searching for the cause, he found a pinched wire on the passenger side valve cover gasket, (caused by his people when they did the gaskets,) so he fixed that free of charge. Replacing the fuseable link with an inline 30Amp fuse after the repair, allowed me to drive the truck for a week with no issues.2) The inline fuse blew again, leaving me stranded. I had it towed back to the shop, and had him search through the wiring again. This time, the wiring that connected the battery to the starter had finally become corroded enough, to completely disconnect power to the system. A simple cleaning of the connection here, and replacing the fuse, allowed the truck to run again, for another week.
3) Inline fuse blew AGAIN. This time, my Distributor had needed replacing, so I asked him to do that as well. During this repair, he found a wire that had been pinched by intake manifold work previous to me owning the truck. He taped that off, and made sure it was connected properly. He also put all the engine compartment wires into the plastic spaghetti to keep it any of them from grounding out on the engine. Truck ran great with the new Distributor, and ran for a day and a half.
4) Inline fuse blew again. He CURRENTLY is working on it at this point in time. I need help here.
The inline fuse, in every case listed above, would blow, causing the entire dash to blackout, no power to dashboard or ignition. However, the plunger for the headlights continued to work, and when activated, it would activate the driving lights, and headlights, and the high beam switch on the floor would cause the headlights to turn bright as expected, even with the fuse blown on the inline fuse. I have checked all the fuses in the interior of the truck, and none of them are burned/blown, which leads me to believe the issue is in the engine compartment side of things. The fuse would blow at random times, not seemingly dependant on engine speed, or whether you would be moving or not – as it has blown on both. When the fuse blows, or is about to blow, all the lights in the dash get very bright, the Tempurature Gauge goes to max, the Volt Meter jumps to full 18V, windows work 2 – 3x as fast (overvoltage I suppose) and the truck will only move at about 10mph, and buck forward and back if you attempt to go any quicker then that.Please, tell me what I can do! I love this truck to death, but not being able to drive it because it can strand me at any point in time is not very encouraging.
What can I do? I would like to just have it be something very easy, like the voltage regulator in the Alternator, (Which, I suppose would make sense….) but if it isn’t bad all the time, how can I test it?
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GM Alternators are usually selfregulated (regulator is builtin). If you are actually seeing high voltage the regulator must be failing perhaps heat related. I would replace the alternator.
Appreciate the tip!
Further diagnosis I got before work:
Replaced the inline fuse with a jumper wite. This would cause the truck to run, but the wire would get hot. (Extra resistance somewhere?) removing the wire after truck starts, causes the engine speed to jump around 500rpm higher, which is strange as it is carburated. Further, when the jumper wire is connected, and I disconnect the alternator when the engine running, the engine dies. (Does not run off battery. Strange?)
So I can look up a wiring diagram, Which pickup and engine do you have? Full Size? V8? You already said carburetor equipped.
Ah! I knew I forgot something in the first post.
1983 GMC Sierra Classic, 305 V8, Quadrajet Carb, H Vin Engine.
C1500 1/2 ton, 2RWD, 5.0LHi.
I would start by checking all you chassis grounds. Look for corrosion or if any have disconnected.
Do you see a ground wire going from the negative on the battery to the chassis of the truck?
What model exactly is the truck?
It almost seems to find the problem some systems will need to be eliminated as the root cause.
Is it possible there is a fuse installed with a current rating greater than specified by GMC?
Is there any correlation to the fuse blowing and rain?
Perhaps split insulation on a wire and moisture acts as the path to ground?
I do not recall if the 83 has electrical fans or engine driven cooling; if electric, does the secondary fan getting called for have an affect?
Does the truck have power windows or locks? If so what is the condition of the flexible conduit between the door and body?
I am just trying to think of high power devices that might cause the issue.
Does the truck have a trailer electrical connection, maybe inspect the condition of the sockets and wiring.
Has any aftermarket lights, snow plow connection, or a winch been installed?
What is the condition of the under hood fuse box cover? Any chance of water intrusion due to cracks or not sealing completely?
[quote=”BigDanIL279″ post=148739]It almost seems to find the problem some systems will need to be eliminated as the root cause.
1)Is it possible there is a fuse installed with a current rating greater than specified by GMC?
2)Is there any correlation to the fuse blowing and rain?
3)Perhaps split insulation on a wire and moisture acts as the path to ground?
4)I do not recall if the 83 has electrical fans or engine driven cooling; if electric, does the secondary fan getting called for have an affect?
5)Does the truck have power windows or locks? If so what is the condition of the flexible conduit between the door and body?
I am just trying to think of high power devices that might cause the issue.
6)Does the truck have a trailer electrical connection, maybe inspect the condition of the sockets and wiring.
7)Has any aftermarket lights, snow plow connection, or a winch been installed?
8)What is the condition of the under hood fuse box cover? Any chance of water intrusion due to cracks or not sealing completely?[/quote]
1) I am not sure – I do not have an original factory diagram/electrical spreadsheet that tells me what fuses need to go where (short of the interior fuse block, of which all fuses appear to be correct.)
2) The fuse would blow rain, or sun. I believe the first time the fuse blew, it was sunny and hadn’t rained for quite a while.
3) It is possible – I’ll need to go through all the wiring to check.
4) ’83 has the Engine driven fan – which does work. New fan clutch recently installed.
5) Truck has Power windows, and power locks. Drivers door lock cylinder wobbles around (I believe the piece that holds pressure on the lock on the interior of the door was not installed correctly by previous owner.) Using the power lock/window switches in the drivers door, the drivers lock mechanism does not fully lock when pressed – I believe this is a separate issue that I need to get into the door for anyway, though. Window motors do run very slowly, compared to a modern car. Combination of old connections, with old parts? Sounds like something to check into, for sure though. The window runs/channels are all dry rotted and crumbled, so water has definitely been inside the door. The connections through the door/body appear fine for what is exposed – I’ll need to get into the door to assess further.
6) There are no trailer electrical connections on this truck (as far as I am aware.) At least, I haven’t tried to trailer or connect any wiring in the back. Crawling under the back end when doing shocks, I did not see any wiring hanging or tucked along the bed/frame.
7) This truck does have two aftermarket lights mounted to the front bumper, however, they have not worked since I bought the truck from the previous owner. The switch for these lights, whether on or off, have not previously caused any issues.
8) The underhood fuse box? There is a fuse block that interfaces with the interior of the vehicle, on the drivers firewall. The wires all enter there, and it is very grimy/greasy from years of neglect. This is something I may want to investigate further. Cleaning out the gunk, and finding some way to seal the wires for peace of mind, if nothing else.
I was able to find these diagrams on AutoZone, but nothing for the H Code 305 under the hood.
Both the Word format and Acrobat Reader format attached.
I will continue to look for the engine electrical diagram and post if found.
Update: Just for kicks, we threw another 30Amp fuse on the line that runs between the other inline fuse that replaced the fuseable link, and the alternator. On test drive, the truck blew the new fuse between the alternator and everything else. Truck did not lose power, however, Oil gauge and Coolant Temp Gauge do not work correctly. Possibly has to do with repeatedly being over volted when the fuse blew previously. This I will need to look into later.
The Voltage Gauge slowly drained down, as the truck ran on battery only, and no Alternator to recharge the system. Truck was running for about 20 minutes before I returned to the shop so I wouldn’t get stranded with a dead battery. When turned off, the truck would turn back on, no issues. It appears we have isolated the problem to the wire that runs to the Alternator, and any wires that branch off of it.
I’ll keep updating this thread as we find things, and what we ultimately do. Hopefully it can help someone else.
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