Wiring

Tiny
TONYG129
  • MEMBER
  • 1997 CHEVROLET BLAZER
  • 150,000 MILES
I think ive narrowed down my problem to a bad ground somewhere. Can anyone suggest the best way to find or test for a bad ground?
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Friday, October 14th, 2011 AT 5:50 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
Voltage drop test.
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Friday, October 14th, 2011 AT 6:31 PM
Tiny
TONYG129
  • MEMBER
How is that done?
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Friday, October 14th, 2011 AT 6:43 PM
Tiny
CARADIODOC
  • EXPERT
You're the second person to ask that in less than ten minutes, (and the second person to ask that this year). I'm typing up the description now. Will be back shortly. Same question as for the other person; what circuit are you working in and what is the symptom?
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Friday, October 14th, 2011 AT 7:07 PM
Tiny
TONYG129
  • MEMBER
My truck will not start without jumper cables. When I do hook up the cables it starts almost instantly. There is absolutely no loss of power in the battery while it is sitting. The battery test 12.5 volts when not running. I have tested my starter battery and alternator as well as all fuses for draws and shorts. My last guess is a bad ground somewhere.
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Friday, October 14th, 2011 AT 7:12 PM
Tiny
CARADIODOC
  • EXPERT
Think about this logically. If you have a bad ground, jumper cables won't help. Well, I should ask first, where are you putting the negative jumper cable, on the battery or on the engine? Current has to go through that ground, (and the rest of the circuit), regardless of whether it's coming from your battery or a different car and jumper cables. The only thing that's being bypassed with jumper cables is the connections on your battery. The story I'm typing up about voltage drop tests isn't going to help because GM insists on using those side post batteries with connections you can't access to take measurements. What I would suggest is taking both battery cables off, cleaning the connections, then making sure they're tight. You may want to also remove the negative cable from the engine block and shine up that terminal with sandpaper.

Some other things to consider are if the battery is getting old it can still measure fully charged but it will lose its capacity as the lead flakes off the plates, the battery could be too small, or the worst one by far is people who poke add-on wires under the battery cables. Those wires lift the terminals so they don't make full contact with the battery.

You should also measure the battery voltage when the engine is running. It must be between 13.75 and 14.75 volts. If it's low, suspect the generator. Since they started using the current design in 1987, it is real common to go through four to six generators in the life of the vehicle. To reduce the number of repeat failures, replace the battery at the same time. The old battery might work in an older car, but as they age, they lose their ability to dampen and absorb the huge voltage spikes these generators produce due to their design.
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Friday, October 14th, 2011 AT 8:34 PM

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