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Smoking electrical system

Tiny
FISHINJUNKI
  • MEMBER
  • 1997 GMC JIMMY
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 350 MILES
1997 GMC Jimmy, car died and 10 or 12 gauge neg. Battery cable to frame smoked, then the insulation on the park brake cable went up in smoke. There is no sign of any positive wires burnt anywhere. Any ideas as to why the neg would burn and the pos fusible link is good?
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Thursday, February 17th, 2011 AT 8:43 PM

10 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,916 POSTS
Check for a loose negative cable where it is bolted to the engine. Current from the starter won't be able to get back to the battery so it will look for an alternate route. Since the engine is on rubber mounts, that means current will go through a ground strap from the engine to the body or frame, then through the small negative wire to the battery.

Caradiodoc
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Thursday, February 17th, 2011 AT 9:04 PM
Tiny
FISHINJUNKI
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The 1 or 2 gauge battery cable to the engine is tight and clean. There was only about a 2 second try to start, if that long. I am baffled as to why the neg burnt, instead of the pos fusible link. I understand why the brake cable coating burnt off, is because that is the only link from body to frame after secondary ground burnt. I'm also concerned as to why it burned in the first place. I've not found any other burnt wires anywhere.
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Thursday, February 17th, 2011 AT 9:14 PM
Tiny
CARADIODOC
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Grab a digital voltmeter, place it on the 2.0 volt scale, put one probe on the engine block and the other one on the negative battery terminal. You are severely handicapped by the side post terminals because that prevents you from including that connection in the voltage measurement, but if you have dual terminal battery, put the meter lead on the top post. Read the meter while a helper cranks the engine. Anything over 0.4 volts is too high. That means there is high resistance somewhere in that cable.

Caradiodoc
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Thursday, February 17th, 2011 AT 9:24 PM
Tiny
FISHINJUNKI
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The meltdown didn't occur during cranking, it occurred while driving. I have had no issues with cranking at all.
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Thursday, February 17th, 2011 AT 9:35 PM
Tiny
CARADIODOC
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Something is confusing. There has to be a pile of current if it melted the parking brake cables. Did you actually see them smoking or could rust have built up causing the casings to become shredded? The cables would connect the drive train to the frame but electrically those would be very poor connections. Starter current wouldn't make it through those cables but that is the only thing that can draw that much current.

Since the starter is working properly, everything on the engine should be able to be eliminated. That leaves the things grounded to the body. That would be the fuel pump, head lights, heater fan, and wiper motor as the biggest draws. Have you found anything that isn't working?

Caradiodoc
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Friday, February 18th, 2011 AT 3:40 AM
Tiny
FISHINJUNKI
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  • 6 POSTS
The door locks and power seats have been inop for quite some time, there was a short so I removed the breaker to eliminate the draw. There should be no short though, with the breaker removed. The four wheel drive blows a fuse if I attempt to use it, but that hasn't been used in a while either. I suspect a bad motor on the transfer case. All other system operate fine.
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Friday, February 18th, 2011 AT 5:11 AM
Tiny
CARADIODOC
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Hmm. For all those fuses to blow there has to be excessive current. A bad ground wire that causes the battery ground wire to overheat would introduce extra resistance which would lower current, not raise it.

The power locks shouldn't draw any current when the switch isn't being pressed. If removing the circuit breaker solved a battery drain, you might look for broken and frayed wires between the driver's door hinges.

Caradiodoc
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Friday, February 18th, 2011 AT 8:48 AM
Tiny
FISHINJUNKI
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Thanks Doc, that's where I was going to look today when I get back to it.
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Friday, February 18th, 2011 AT 3:02 PM
Tiny
FISHINJUNKI
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I just wanted to thank you for all of your help. Though you did not provide me with solution, you did get me thinking, and back to basics. I checked for continuity between the batt. Pos. Cable and ground, but there was none. Unconvinced, I removed the pos. Batt. Cable from the car to find that it had been grounding out against the frame side of the motor mount. I realized that the only place that such a large short could happen without blowing fuses, or fusible links on the pos. Side. Thanks again, and have a blessed weekend.
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Sunday, February 20th, 2011 AT 4:29 AM
Tiny
CARADIODOC
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Very happy to hear it is solved. Maybe this is a good day to fix the half dozen busted pipes in my house!
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Sunday, February 20th, 2011 AT 4:34 AM

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