Battery wire fire + alternator arcing

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

basscat

Newbie
Joined
Jun 22, 2022
Messages
13
Reaction score
16
Location
Texas
Hello all! Newbie here, 1st post. Learned a ton from this forum already!

1990 Chevy C2500 350TBI
Original owner; literally bought it 32 years ago today!

Was in a wreck in 2008 that damaged front end. The body shop asked what level of repair I wanted (insurance company totaled it) and I responded "lowest cost" and they went heavy on "cheap"! Repaired & drove home and it's sat up ever since. Now I'm getting my hands dirty to get her back in good condition. My latest project was a complete coolant flush & hose replacement. I cranked it up and turned the heater blower on high to top off the coolant level etc. All was good for 10-minutes then the engine bogged & died. At the same time there was severe arcing from the alternator terminal. The smaller wire, from the +battery post to the junction box, caught on fire and melted in two.

After my heart settled I began to inspect. It's my fault for not noticing they didn't replace the fusible link from the +battery to junction block (lots of the front end needed replacing after wreck). But I also noticed corrosion & breakage in the ground wire to the fender. The ground from the battery to the intake manifold appears to be good and the ground straps are good (frame to body & frame to engine).

It's been too many moons since my physics classes. Would/could this failed ground wire be the cause of the problem? I did have to brush the negative cable to make a connection prior to starting. I did notice the corrosion, but replacing the cables was certainly on the to-do list, but wasn't a priority since the truck hasn't left the driveway. I suspect if the fusible link was installed it would have simply done its job and burned out. But I'm not qualified to understand this properly and hoping more experienced folks might be willing to clarify the situation. Initially I suspected the 25+ year old re-man alternator suddenly failed and sent a surge of voltage. I suppose that's a possibility. I haven't had problems with the dash volt gauge showing unusual voltage or unusual behavior and it's been able to keep the battery charged. The battery is a 3 month old Duralast that I bought while working on the truck and later planned to upgrade when I replaced the cables.

I traced the wires to the junction box and to the alternator and down the frame to the starter and found nothing noticeable regarding possible shorts. I did not use a multi-meter (yet). I appreciate any and all assistance in narrowing the cause of this problem. Thanks!

You must be registered for see images attach


You must be registered for see images attach


You must be registered for see images attach


You must be registered for see images attach
 

HotrodZ06

GMT400 Collector
Supporting Member
Joined
Apr 30, 2016
Messages
172
Reaction score
217
Location
Lake Texoma
Might take the alternator to orielly's or autozone and have them test it and see if it shows bad, my guess would be the nut wasn't completely tight and possibly the fusible link compromised by the accident. May just need a new fusible link.
 

basscat

Newbie
Joined
Jun 22, 2022
Messages
13
Reaction score
16
Location
Texas
Might take the alternator to orielly's or autozone and have them test it and see if it shows bad, my guess would be the nut wasn't completely tight and possibly the fusible link compromised by the accident. May just need a new fusible link.
Thanks! Yeah, I definitely should go have it tested. I did have that alternator terminal disconnected that morning and I suppose user error could have caused the nut not to be properly seated. Would it be uncommon for the alternator terminal to arc otherwise? Even with a potential bad battery ground?
 

Erik the Awful

Supporting Member
Supporting Member
Joined
Aug 9, 2019
Messages
7,814
Reaction score
16,069
Location
Choctaw, OK
If the smaller wire on your negative cable burned up, your larger cable didn't have a good connection and you're forcing more current through the smaller cable. Replace the barely-adequate factory wires with good wires, clean the connections, install your missing fusible links, and ensure all your ground straps are in place.

The more dangerous problem is that it sounds like you have a major short to ground in your truck somewhere, and it sounds like it's not going through the fuse block.
 

basscat

Newbie
Joined
Jun 22, 2022
Messages
13
Reaction score
16
Location
Texas
If the smaller wire on your negative cable burned up, your larger cable didn't have a good connection and you're forcing more current through the smaller cable. Replace the barely-adequate factory wires with good wires, clean the connections, install your missing fusible links, and ensure all your ground straps are in place.

The more dangerous problem is that it sounds like you have a major short to ground in your truck somewhere, and it sounds like it's not going through the fuse block.
Thanks for the feedback! Typically I think about what changes were made that could've caused a problem. The only electrical modifications made were: (1) cleaning the negative cable terminal to get a connection (wouldn't crank otherwise), (2) unscrewing nut from alternator BAT terminal and re-tightening (the ring terminal may have seated incorrectly despite tightening the nut good).

The smaller wire on the negative cable didn't burn up. It's corroded and frayed from age and twisting. There are no signs of heat or arcing. Absolutely going to replace. It was the smaller positive cable that burned up. From the alternator to the junction box there's a fusible link. I haven't tested it, but I would've thought it would burn before melting the un-fused smaller wire from battery to junction box.

The incident occurred after 10-minutes of idling. Theoretically the vibration could've loosened the terminal nut enough to arc. Would you rule out that being a potential cause of the smaller positive cable burning?
 

basscat

Newbie
Joined
Jun 22, 2022
Messages
13
Reaction score
16
Location
Texas
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?

You must be registered for see images attach
 

HotrodZ06

GMT400 Collector
Supporting Member
Joined
Apr 30, 2016
Messages
172
Reaction score
217
Location
Lake Texoma
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.
 

basscat

Newbie
Joined
Jun 22, 2022
Messages
13
Reaction score
16
Location
Texas
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.
Isn't that bolt the primary ground for the alternator?
 

HotrodZ06

GMT400 Collector
Supporting Member
Joined
Apr 30, 2016
Messages
172
Reaction score
217
Location
Lake Texoma
Isn't that bolt the primary ground for the alternator?
All the mounting bolts provide a ground for the alternator, specifically clamping the alternator to the bracket. Not justifying leaving it out, I just don't think that is your problem, but I could be wrong only testing can verify what the problem is.
 
Last edited:
Top