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Old 11-03-2005, 12:35 PM
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Battery connected backwards

My dilema involves connecting a battery with the negative cable on the positive post and the positive cable on the negative post. No arcing, but lots of smoke and the main power feed from the alternator to the fuse box is cooked. Did we kill the alternator? How far back do I have to replace the wire? It appears that the burn only goes back to the fuse panel. The vehicle is a '68 Chevy pick up. Side terminal battery was replaced with an Optima battery with the posts being opposite of the battery being replaced.
Thanks for the help.

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Old 11-03-2005, 04:26 PM
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Doc here,

As far as frying the alternator, you'll have get it running again to tell if it died...or pull it and have it tested..

Not sure if 68 vehicle manufactures were up to installing Fuse links or not yet, May have been, so you might need to track those down.

You will need to now, unwrap the tape from the wire bundle going to the firewall (and beyond) and inspect it carefully for burned and melted insulation from the shorted main wire..Repair ANYTHING that looks slightly suspicious. Do this carefully...the future of your rod depends on it, if it's not to catch on fire!

If you had any Digital systems (CD/PLAYER) and digital clock, these will need inspection also..

Reverse polarity on digital items will kill them..on more expensive items They may have a Zenier Diode inside the unit, where the power wires go through (it's a little glass diode on the power wire to ground)

It 's job is to crowbar to ground on a reverse bias of 12 volts permanently..so you just can't re~Fuse on a reverse polarity, and will blow the fuse right off every-time you turn it on..

To test it open the unit , locate the diode, and lift either end from the circuit..if the unit functions again replace the diode...($2.00 at the electronics store) This is where most people throw expensive units away, because the "Just blow fuses every-time they turn them on"..It's usually an easy $2.00 repair..

Other items to watch for that may have been effected, are If you have HEI, the module could be aced..and keep an eye on Tach and gauge instruments if they have linear type op amps for senders / Metering devices..

In Future, I would install fusible links on every wire that goes back into the system at the solenoid, and the alternator big red wire, and you won't suffer this kind of damage (or as bad anyway)

And remember, FUSE LINKS never are installed inside a vehicle compartment, the work by heating up and melting, can set interior parts on fire, melt plastic, and the fumes are toxic in a closed cabin..



When you get it running again, measure across the battery, should read about 11.90 to 12.5 volts not running..then start it..it should be 13.95 to 14.4 if the charging system is working, and not rise and fall with RPM's..

Good Luck!

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Old 11-04-2005, 06:36 AM
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Doc:
Thanks for the reply.
Last night while digging around, I found that the coax wire from the antenna to the radio was cooked. So bad it burned through the new carpet. The antenna was connected to the CD/radio but when I put power on the head unit, it still works and will play CD's. No radio as no antenna.
Is there a way I can check the HEI? The key was not on when the meltdown happened. I am taking the alternator to the shop today to have it tested. While I am at the shop, I will buy a handful of fusible links.
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Old 11-04-2005, 04:03 PM
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Doc here,

The links are a good safe Idea!

To test the HEI, pull the module and take it with you when you test the alternator....OR wait until it is all repaired and just run it...If it won't start or runs poorly (or different) get another.

On that stereo, I fear you may not be able to hear any stations again! Try another Antenna, or a long piece of wire..see if you can pick up ANYTHING at all..A failure of this type (melted coax wire) can cause the RF amplifier in the receiver to fail...(first stage of he radio's front end..) If it won't pick up any stations..this may be the case.

The problem when reverse polarity occurs is, you have power on the ground side of the vehicle, and that goes everywhere and is un~switched..and unfused. If you have an item that travels on ground normally (like the antenna for instance) or has a high resistance to ground through the component..the power will short..(as did the coax)

In other words, If the insulating washer were bad or partially shorted (which would hardly be noticed on properly directed power) on the antenna, it would feed power back through the RF amp inside the radio, to ultimately the power side..creating a dead short going that direction..Like a diode..it is isolated one way (normal polarity)..the other it conducts current in the forward direction...(reversed polarity)

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