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 Small Electrical Fire

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59 Blue Bomber

Posts : 199
Join date : 2010-06-05
Age : 46
Location : Corbett, Oregon

PostSubject: Small Electrical Fire   Sun Jul 10, 2011 10:30 pm

I had quite the scare recently, while cleaning the car for our annual Corbett Funfest Fourth of July Parade. I saw smoke under the dash. I wasn't even working anywhere near the dash when I spotted it. I managed to get the battery cable off, but not before burning the tip of my finger in the process.

After the smoke cleared, (no pun intended), the red and yellow 10GA wire from the battery/ voltage regulator completely melted/ fused together. These two wires feed the ammeter in the dash. Needless to say the ammeter is now fried! I have no earthly idea what caused this to happen.

I suspect it had something to do with the ignition switch, but this is mere speculation. I carefully, (after it cooled down) separated the harness coming through the firewall and up under the dash. No apparent damage to the other wires in the harness, but termination of the red wire (which connects to other accessories in the harness) was completely melted/ burnt to a crisp. I pulled out the fried wires and connected the red/yellow wires together (that feed the ammeter) and all is well.

I am mystified as to how this came about, since I have not even messed with the wiring under the dash. Although it appears someone else did in the past, with the crimped spade connectors on the ignition switch and radio. Perhaps one of the wires had a bare wire showing and shorted out, I don't know.

What I did find out was there is NO fuse connecting anything concerning the battery and the voltage regulator or ammeter. Just straight connections! Anyway, it is fine now, from what I can tell, but iam now on the hunt for an Ammeter for the dash, since I like to know what the generator battery codition is while I'm driving! If anyone knows..about the Ammeter or the probable cause...I'm ALL ears. again...Mystifying!

Scary stuff, because this could have happened while I was not home..I don't EVEN want to think about that!
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Posts : 304
Join date : 2008-07-03
Age : 74
Location : Levittown, Pa

PostSubject: Re: Small Electrical Fire   Tue Jul 12, 2011 12:12 am

Chad.....Scary stuff! Glad that the only damage was your finger and a fried ammeter. There's a reason those wires are bigger than others. They carry the amperage of the entire car, except for the battery to starter cable. My first thought was a short circuit that isn't controlled by the ignition switch (horn, dome light, stop lamps, clock, and lighter.) All those are fuse protected though. The only non-fused circuit is the headlamp switch, but it has a built-in breaker.

The way I read the schematic, The yellow wire feeds the ammeter, picking up battery current at the junction block that's attached to the horn relay. The red wire on the ammeter returns current to the batt terminal of the voltage regulator. On the way, it branches off to the headlamp switch, the ignition switch, the back if the fuse panel, and the lighter. I would troubleshoot those wires for a short. Something was drawing alot of current to melt those wires, and not blow a fuse. If as you say, someone was messing with the wires on the back of the ignition switch, start there.

That could have been a much bigger disaster if you were not around to catch it. A good solution is one of those battery shut-off terminals on the negative post. I may have an extra ammeter, but you realize your sending this old man up into my workshop attic at about 150 degrees. Have pity!.....John
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Posts : 152
Join date : 2010-04-12
Age : 51
Location : Vernon, B.C., Canada

PostSubject: Re: Small Electrical Fire   Tue Jul 12, 2011 7:58 pm

Yikes!! My guess is youve probably got some melted wire somewhere. When I rewired this winter I saw a whole lot of questionable stuff-melted, rubbing through grommets, cracked and the like. I guess it was those hot California summers. Too bad this didnt happen sooner-I bought a dash cluster last month just for the speedo and told the guy to just send the speedo as the shipping was too high. Good luck on the troubleshooting! It was probably just a gremlin anyway.
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Join date : 2008-05-23
Age : 44
Location : Denmark

PostSubject: Re: Small Electrical Fire   Wed Jul 13, 2011 5:49 pm

As John said - those wires carries all the current, exept for the strater. As far as i can see they are much heavier than the rest (that i assume didn't melt), and to me that indicates that the short was on the heavy gauge section (from the battery to the ammeter and back to the junction box). Maybe you can tell from the wires (how bad they melted) how far from the battery it happened (it could be internal in the ammeter). Anyway, i surgest replacing the entire heavy gauge from battery to junction box, adding a fuse (the kind that is used for heavy car stereo installations) of 50 or 60 A rating - as close to the battery as possible. This should protect against most shortcircuits.
Also check for poor connections, since that is bound to cause heating during heavy current draw, and may melt insulation causing a short circuit. An easy way to check this : Turn on the dome light (or other light). Now turn on somthing that draws some amps - say the cigarette lighter - and watch for drops in light intensity. Any significant drop in brightness would indicate that a common current path (the heavy wire to the ammeter) has too much resistance.

Although the voltage is much too low for any risk of electrocution, a standard car battery has enough current capability to melt a wrench. I saw this happen once, when someone tried to remove a battery from an old stationary battery rack, and accidently touched the metal casing with the wrench while unscrewing the positive terminal. The negative terminal was still connected to the casing, and the wrench welded to the metal casing, and started getting red. I had to remove it with a hammer .

While shopping for my engine rebuild i came across a large main switch for the battery - i guess this was my wake-up call to go get it installed lol! .
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