Ignition

Tiny
MARCUS DENNARD
  • MEMBER
  • 1992 JEEP CHEROKEE
  • 92,000 MILES
Left ignition on over night now the car is dead no power. Got jump off with cables. Cables became hot and started smoking. No power to car though. Engine fan was attempting to turn but there were no key in ignition.
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Tuesday, September 20th, 2016 AT 2:53 PM

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Tiny
CARADIODOC
  • EXPERT
The jumper cables were connected backward. The sparks when they were connected should have shown that. Now you should have a number of blown fuses, I hope. All of the computers have a diode in them between the 12 volt feed wires and the ground wires. Diodes are a one-way valve for electrical current flow. For this application, they are installed backward so it is like they are not even there. When the jumper cables or the battery cables are connected backward, those diodes become a dead short. That causes the fuse for that circuit to blow, thereby saving the rest of the circuitry.

1992 was right in the middle of when they started putting a fuse box under the hood as well as inside, so when you are checking them, be sure to look in both places. If there is no fuse box under the hood, there will be a number of fuse link wires. Those are spliced into the regular wire they protect but are a little smaller in diameter. Also, the insulation will not burn or melt, so don't replace them with regular wire. Auto parts stores sell replacement fuse link wire by gauge and color to denote its current rating. The length in the vehicle is not important so the piece you get will be long enough to be cut into two or three pieces for multiple repairs. I do not know where those fuse links will be on your vehicle, but on the minivans, there was a bundle of about two dozen going around the left strut tower. They will be dull, not shiny like the rest of the wires. The common colors are green, gray, black, orange, and white.

Even if you do have an under-hood fuse box, you most likely will still have a large fuse link for the output wire from the alternator. Alternators have six diodes that are also backward. They have an important job to do when the alternator is, alternating, but when the engine is stopped, they prevent the battery from discharging through alternator. With the cables reversed, those diodes will also be "forward biased" and appear as a dead short. Fuse link wires take some time to burn open, so it is possible those diodes have been seriously-overheated and are now shorted. We will cover that if it becomes necessary once you get the engine running.
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Wednesday, September 21st, 2016 AT 1:57 AM

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