Would you please advise me in this matter. I accidentally connected the wrong terminals to the battery some years ago. I am beginng to work on the car. When ever I turn on ignition the fusible link burns out. Can someone tell me or email me on the procedure to track the problem. Any advise is appreciated.
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Abe
Try disconnecting the alternator and see if that fixes it. The diodes in the alternator may have gone south. MM
concur, diodes (or rectifiers) fail short as often as open. although they should have had no trouble withstanding reverse polarity at 12 volts, as rectifiers their job is to block the reverse voltage as well as conduct. so there may be another culprit... since you must turn on the ignition to cause the problem it is either conducting huge current through the ignition switch itself, or a relay that is energized by the ignition circuit is providing power to something that is shorted.
there are "short circuit" finders on the market, cheap. replace your fusible link with a 12v light bulb, this will limit the current and allow it to flow through the short without burning anything up (use something smaller than a headlamp...) then you can start tracing wires with the short finder until you find one with the bulk of the current flowing in it.
each rectifier must withstand at least as much reverse voltage in normal operation as forward voltage. a car alternator uses full-wave rectification, but in a half-wave circuit the rectifier must withstand reverse voltage at least double the forward voltage.
connecting a battery backward would cause the current to flow backward through the alternator stator windings, assuming there is no relay to prevent this. this current flow could conceivably exceed their current capacity, overheat them and burn them out that way.
If some rectifiers failed and became shorted, which is not uncommon, it is conceivable that enough current could flow backward again with the battery now connected properly, through the alternator stator and melt the fusible link.
the obvious fix is connect a **12 volt** light bulb between the battery plus terminal and cable, (or in place of the fusible link will work just as well) disconnect the alternator wire at the alternator, turn on the key, and see if the light comes on. if not, reconnect the alternator, if it comes on then, the rectifiers or something else in the alternator is indeed the culprit. if the light comes on just as bright in both cases, it is not the alternator, or at least the alternator is only one problem among many.
by using a light bulb in series, no more current will flow than the light bulb consumes, so choose a reasonable one, like a parking lamp (1157 etc) NOT a headlight or something ridiculous.
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