How's this for stupid...
 

I'm changing my oil yesterday in the '94 wagon and taking the cap to the filter off and I'm spinning the cap with the socket and extension which then falls into the engine area. I can see it and reach down to grab it and it arcs out really bad! I thought it would start a fire! I reach down again and touch it and it arcs out again badly. I look closely and see it is wedged against the positive pole of the starter and every time I move the extension it shorts to ground against the engine!:eek: I finally disconnect the battery and get the socket and extension out but now my dash lights are out but the fuse is still good. Any thoughts? Is there a second fuse box somewhere? The socket took some major heat and melted one side!:eek: Live and learn right?

No, you weren't stupid, just got complacent for a moment as we all have. It sounds as if your dash lights took some current through the chassis when the cannister dead shorted the battery, but, not knowing the wiring of that circuit, I don't know. That the dead short and loss of dash lights took place at the same time I would pull the easiest bulb to get at and see if it's still good; also, look for any burned small diameter wires, though any burn through could have taken place in a harness or connecting block. Any other electrical problems develop such as parking lights, etc?

Not that I can tell right now. Wait - I forgot to check my brake lights. I'll check those at lunch.

Now you understand why that first repair step is always written in the manual.

1. Disconnect the battery

- we have all taken this short cut.

I would never think to disconnect the battery when changing oil. Do you really think the MB techs take the time do that for an oil change? DTF, I'll bet you couldn't do that again if you tried.

No Kidding! I'm lucky that I didn't get shocked touching the extension and arcing. I can't figure out why I didn't. It would've knocked my silly. I go back up to the house to get the wrenches for the battery and the wife says " Everrything all right out there?" I say ' yeah - great!" Teaches me to not have a beer in my hand when changing the oil. Still have dead dash lights though...

the only shocks you can get from a DC system are from a circuit amplified by the coil (plug wires) or dragging your ass across the seat and building a static charge. you can touch both battery posts at the same time with your fingers and nothing will happen. in an AC system (you're house wiring) this could kill you.

12 volts but capable of extreme current
 

The hazard is shorting metal across an unprotected (unfused) circuit and having it melt onto (human) body part.

Like jewelry.

I dont know on what study you base that on, high DC current at low voltage can and has known to hurt people, put your tongue across the terminals on a 9 Volt battery, and it does not provide a lot of current

That's an old trick.
Works better than Viagra. :D

The fallacy of this kind of thinking is that the resistance enters the formula. With 12 Volts and normal skin resistance being in the thousands of Ohms the current able to pass is in the tens of microamperes. This means you will not be able to pass high current thru human skin with 12 Volts (high current being defined as amperes).
In other words, 12 V won't hurt you. If it could harm you there would be warning stickers all over the battery and the area around the battery and the cigarette lighter and every place like in an electrical breaker box or switch panel.

Electrical safety classes state that voltages above 24 Volts are considered dangerous.
The statement/warning about jewelry is very applicable when it comes to a storage battery however.

True, but what about conditions that lower the skin's resistivity, ie sweat, rain, wet clothes, engine fluids and puddles, etc. Don't think for a minute that you cannot get seriously hurt from 12 volt battery voltage. Remember, that storage battery is capable of delivering several hundred to over a thousand amps when shorted... It takes about 70 milliampres to stop the human heart, IIRC.

And the jewelery... Ask anyone who has had the displeasure to have a piece of jewelery (a ring, for instance) short out on a 12 volt circuit. I have an employee who refused to remove his wedding band. One day, while tightening up a battery (12 volt 4D) with a crescent wrench, he had the misfortune to let the ring complete a circuit from his wrench to ground... Several weeks of painful recovery from surgery was his constant reminder...

Remember Ohm's law
 

Current = Voltage divided by resistance.

If battery voltage is 12 volts and the typical resistance of the human body from hand to hand is about 1 Megohm then the current that flows is 12 microamps if my math is right.

More if you have sweaty hands but nothing near what it would take to cause heart fibrillation.

Refer to http://www.allaboutcircuits.com/vol_1/chpt_3/4.html for what lethal currents might be.

That is one GREAT site.

thanks.

I'm sorry but you don't understand the laws of electricity :rolleyes: I tried to explain Ohms law but you didn't read it well, or comprehend that even with wet hands the resistance of the human skin can't conduct amperes of current at 12 Volts.
IT DOESN'T HAPPEN. CAPICHE?
Dont mislead people!

Well, 12VDC at hundreds of amps (short current of a car battery) needs to be well respected. For obvious reasons, the terminals of a starter aren't fused. Very bad idea to wear a watch or wedding ring around this area. A much better idea is to remove the battery from the circuit.

It's a combination of voltage, amperage, and the resistance of the skin that shocks/kills/char-broils. I once worked with UPS system with 380VDC and amps so high that a wedding ring could vaporize and blow your finger right off. And just a few volts, under certain conditions (that you aren't likely to see outside of a hospital) can definitely kill.

AC, you can let go if your heart doesn't stop first. Hi-v, Hi-current DC, you just hold on and smoke until someone knocks your body out of the circuit...

The resistance of your tongue is low enough to cause injury if it gets across a 12 V battery. Thats why the terminals are all further than a tongues length apart:rolleyes:

Shouldn't that terminal have a rubber boot on it?
 

Shouldn't that terminal have a rubber boot on it?

1- You should go to wally world or any boat shop and buy some liquid electrical tape.
2- REMOVE THE BATTERY! :)
3- put a couple of coats of liquid electrical tape over the terminal

This will help keep this from happening again.

-Jim

25 years ago when I worked for SteveBFL's shop I was replacing a mechanical fuel pump on a 114 body 4cyl. MB and had the misfortune of completing a conveniently located 12V electrical circuit with 180 deg. of my watch band. It heated up quite nicely and given the tight confines required a bit of time to remove my hand from the offending circuit (burned the stink out of my wrist but didn't require amputation). Good thing I hadn't cracked open the fuel lines yet. Now I am quite careful to remove ALL jewelry BEFORE I start to work on my cars. Mark