Battery wire fire + alternator arcing

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DerekTheGreat

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Sorry about the snafu with the body shop, but cool truck! What's its story? Like, did you buy it off a lot or custom order it? Buy it for a specific purpose? Why a 3/4 ton over a 1/2 ton? What options does it have? Pretty neat that you kept it all this time. It's the same color scheme as my '89. Stick shift?
 

basscat

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Took the alternator to O'Reilly and it passed their test. I did notice an obvious uneven seating at the base of the terminal stud. But that didn't prevent me from being able to tighten it good prior to the incident. I threaded a nut on by hand and was barely able to slide the edge of a thin piece of paper between the nut and that seat. I'm sure with a wrench it would close the gap. Some of that grommet material is warped from the arcing, but it seems the alternator should be ok. The nut wasn't loose when I removed it after the arcing either. The rabbit hole gets deeper
:)
I found a correct bolt at Ace Hardware for the one that was missing.

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@DerekTheGreat -- thanks! I found the truck through a dealer inventory search and had my dealer arrange to have it sent to his location. If my memory is correct, the only options it did not have was the engine block heater and perhaps rear window defrost? Maybe those were options I saw that were available for other models,,, not sure. But it's loaded otherwise. It's the C6P heavy 8-lug 3/4 ton with the Muncie 4-speed granny transmission with 3.73 rear-end. I still have the window sticker believe it or not! $16,828 !!
I went with the 3/4 ton because I made money in the summer hauling hay while going to school. I remember my grandfather asking me why I wanted to bounce around in a stiff truck and always shift gears. Shifting those gears is what I've missed most and is my inspiration to get this back on the road :)


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RichLo

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Since your alternator tested fine I would put it back in and replace all of the burnt wiring then put an ammeter inline between the alternator and battery to see how much your actually pulling from your alternator.

Here is a cheap 60 amp option, do not run this full-time on a street vehicle! This is for diagnostics only since volt-ohm meters usually max out at 10 amps unless you invest in a pro-grade unit.


This will tell you if there is something else that is shorted to ground and pulling amps when the truck is running. And you can turn things on and off to see what may be pulling heavy current.
 

Hipster

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It's my truck. I take full responsibility. But I mentioned "they went heavy on "cheap"!"

Was about to pull the alternator to have it tested when I noticed this. The body shop didn't install the bolt from the engine to alternator. Is my understanding correct that the alternator gets its ground through the engine and the vibration was causing the alternator housing to separate from the engine which led to the arcing & fire due to intermittent loss of ground?

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As a body guy, just trying to get my head around why a bodyman would remove an undamaged alternator and re-install the same one. Things like an alt don't typically need to be R&I'd in the process unless there's physical damage and then it gets replaced. Maybe it's new/used to the truck. idk.
 
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DerekTheGreat

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@DerekTheGreat -- thanks! I found the truck through a dealer inventory search and had my dealer arrange to have it sent to his location. If my memory is correct, the only options it did not have was the engine block heater and perhaps rear window defrost? Maybe those were options I saw that were available for other models,,, not sure. But it's loaded otherwise. It's the C6P heavy 8-lug 3/4 ton with the Muncie 4-speed granny transmission with 3.73 rear-end. I still have the window sticker believe it or not! $16,828 !!
I went with the 3/4 ton because I made money in the summer hauling hay while going to school. I remember my grandfather asking me why I wanted to bounce around in a stiff truck and always shift gears. Shifting those gears is what I've missed most and is my inspiration to get this back on the road :)

I dig the story! Looks like you were specifically looking for a 350 8 lug stickshift truck, cool. :) Also dig that you've still got the window sticker. It is loaded, I've only ever seen one early regular cab truck optioned with rear defrost. I added it to my '89. I had a C3500 with a 454 and that same SM465 "dump truck" transmission. Wish I never sold it. If you'd ever like to trade trucks (mine is the '89 in my signature, same as yours just half ton, five speed, 4x4 and short box) or sell that one, let me know. I've got a soft spot for 2500's or 3500's with clearance lights and do-it-yourself transmissions.
 

basscat

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I think most people leave that one out when they replace an alternator because its hard to get to, so I wouldn't think that would be the culprit. If the fuse box wire burnt up I would be looking for something it powers drawing too many amps. That may be the root cause of it all.
Based on @HotrodZ06 comment I grabbed a multi-meter and "tried" to test conductivity to find a short? I'm probably doing it wrong and don't understand how it's supposed to work. Both + & - battery cables disconnected and alternator is off the truck. I wanted to see if the fusible link between the alternator and junction block was good or making conductivity. The audible chirp confirmed conductivity (+ lead from alternator end to + terminal on junction block). I then touched 1 probe to the + alternator cable and the other probe to the junction block's mounting bolt head to firewall and got an audible chirp. I then starting moving the probes to multiple locations along the firewall such as the windshield wiper mounting bolt to firewall and the + alternator cable and got a chirp. Does this indicate that a positive wire somewhere is grounding?

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Frank Enstein

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Based on @HotrodZ06 comment I grabbed a multi-meter and "tried" to test conductivity to find a short? I'm probably doing it wrong and don't understand how it's supposed to work. Both + & - battery cables disconnected and alternator is off the truck. I wanted to see if the fusible link between the alternator and junction block was good or making conductivity. The audible chirp confirmed conductivity (+ lead from alternator end to + terminal on junction block). I then touched 1 probe to the + alternator cable and the other probe to the junction block's mounting bolt head to firewall and got an audible chirp. I then starting moving the probes to multiple locations along the firewall such as the windshield wiper mounting bolt to firewall and the + alternator cable and got a chirp. Does this indicate that a positive wire somewhere is grounding?

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Yes it does!
 

basscat

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I appreciate all of the feedback and assistance thus far and hope I don't become a nuisance with my questions :)
I keep thinking I'm doing this multi-meter testing wrong. In my mind I think any non-grounded wire should be open (hope that's correct term) and not visible by the conductivity test until a switch/relay closes the loop. If any of those wires have failed by making contact with the truck then I'd expect to see conductivity similar to if a switch/relay closed the loop.

I've removed all terminals from the junction block. I then touched one probe to the smaller + battery cable and the other end to the same wire's ring terminal. I got a loud constant chirp from the multi-meter as I'd expect. It's a straight wire with no other connections. I then moved the probe from the smaller + battery cable to the negative battery cable (battery is not on the truck) while maintaining the connection of the other probe to the ring terminal. Surprisingly, to me, I got a split-second "grunt" sound from the multi-meter. Okay I yanked that wire completely out of the truck. Next I did the same test with the alternator wire by touching one probe to the end that connects to the alternator and the other probe to the wire terminal that goes to the junction box, but it's disconnected. As expected I received the loud constant chirp confirming conductivity. I then moved the probe from the alternator side and touched it to a bolt going into the firewall with the other probe still attached to the ring terminal. Surprisingly I'm still getting a constant chirp. I've not pulled back the tape/loom that houses the cabling from the alternator to the junction block. But the service manual shows it to be a direct connection with no other splices/junctions.

I probably need a lesson on 12v or meter testing :) I can't understand why there would be a chirp from the terminal to the firewall if those 2 aren't physically connected anywhere. There are more wires from the junction block that are also chirping when I touch a probe to them and another to the firewall. But I'm going from left to right on the junction block trying to isolate each one and reading the wire diagram to dig deeper.

Any ideas of what I'm doing wrong or what I'm not understanding? Thanks!

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