I find myself repeating this at least once or twice a week, so I'm broadcasting it loud here in hopes that many people will see it.

Folks, NEVER touch a tool to either end of the positive battery cable while the negative battery cable is connected. If you must change a battery, disconnect the negative battery cable first and reconnect the negative battery cable last.

If you fail to follow this order and make one wrong move with the wrench, it will cut through your hand like butter when it fuses in two, and impale anyone who happens to be standing in just the right place. Even worse, the spark created from this event may ignite fumes around the battery, causing it to explode and blind you.

In fact, this order is required for any hot-at-all-times load. Starter solenoids, back of the alternator, headlight switch, un-switched fuses (brake lights, cigar lighter, etc): disconnect the negative battery cable first, get in there to do what you need to do, then reconnect the negative battery cable last.

If you perform a "parasitic draw" test with a series-connected test light or ammeter, use the negative battery cable. Battery cut-off switches go on the negative post. These trucks are negative-earth vehicles. Do not ignore the negative battery cable. There is in fact such a thing as a positive-earth vehicle, in which case the procedures I've described are backwards - but that is not the case with these trucks and most other vehicles you and I interact with on a daily basis.

Do not deviate from this advice for any reason, no matter how much you're in a hurry, where the vehicle happens to be stranded, what your dad has always done, whether you think I'm full of it, nothing. Pass this on to your kids. There are too many blown fusible links and burnt up wiring harnesses because of people being careless. I have seen some bad dash fires and they are almost always caused by stupid people.

And, no matter how silly you think it looks, always wear goggles when working near a battery. Never underestimate the power and sheer strength of a lead-acid battery. Treat batteries with the same care and common sense that you do with your firearms. They are just as dangerous in the hands of a careless individual.

Thanks,
Jeff

 

Good post, and sound advice!

Believe what he says. Don't even wear rings or watches around batteries. I turned one wedding ring, and a watch red hot in an instance being an idiot army grunt. I was working on a set of m813a2 truck batteries. I'm lucky they didn't blow up in my face too.

 

A huge +1...Safety first guys.

 

Thank you for the reminder. We all need them once in awhile. Excellent info.

 

I've seen others, and have myself touched a wrench from a grounded surface to the positive terminal (and vice-versa) on a car battery. It makes for an impressive spark show and certainly presents explosion hazards...but to say it will "cut through your hand like butter" seems a bit extreme to me. Has this happened to someone you know? What size battery we talking?

 

Agree with fmc! The minute or so that you "save" by shortcutting can come back to haunt you very quickly. It will take a lot more time and money to fix what you mess up than you'll ever save.
The personal injury electricity can cause is a whole different story. Electrical burns are almost instantaneous and can be really, really wicked!
LISTEN TO HIM!!
Good, sound advice, reps sent.

 

Lets not pick it apart, just take it as sound advice. I melted my 6" closed buck knife in 2, common sense and a 1000 amps is serious, period

 

A really good example of this is Ford. Before 1956, when Ford switched to the 12 volt electrical system, they used 6 volt positive ground.

 

I've tried to beat this into the heads of people at work.
I still see them arcing a terminal by doing it wrong.

The worst in recent history for us was a bank of 4, 8 D batteries blowing up in a crawl space and the kid that was checking them.
He looked REALLY bad and was blind and bruised for several months.

 

It is ignored all to often. With my car audio background, I have seen lots of injuries and damage caused by nit disconnecting the negative wire before working.

 

Yup.. wiring up a CB in the bus and buddy hit the wire with a screw. it wasnt fused at the terminal and it started to smoke. I was working in the area there and tried to pull the wire off the terminal quick like... yeah it turned red as I grabbed it...

 

Thanks for the good reminder Jeff.

I always appreciate you precise, sound advice.

A couple of weeks ago my headlights wouldn't come on. I was about to post for help when I realized I'd get blasted for not having a precise description of the problem. So, I went back out to the garage and started plodding through it and had the problem solved in 1/2 hour. So you helped me fix the problem without even typing

 

Can I disconnect a ground wire in order to reconnect it to a better location (say, my tach ground) if I don't have my negative terminal disconnected? Just a technical question about electricity...I always disconnect my battery because I'm terrified of dying!

Also: whenever I disconnect my battery, I hang it out over the grill and then tape the wire with electrical tape so that the connector cannot touch anything. It just hangs out over the grill. I did it this way because I was worried if I just left it dangling inside the engine compartment that there would be a chance it would touch some metal...and wouldn't that complete the circuit of electricity again?

I'm just now learning all of this...and honestly batteries scare the crap out of me. Which is probably good because it keeps me safe. Hopefully I'm doing it correctly.
Jon

 

I had this happen on a 24VDC system with an Ordnance forklift. positive cable rattled off a battery, and stupid me had tools to try and fix it. The bottom of the foam on the needle nose i was using had a hole in it, and they grounded out on the metal body. Welded them in place with a shower of sparks. Everyone thought i'd died.

 

I've never had a problem with 12VDC but I've been zapped really bad twice and survived both times. Once was 480 volt and the other time was 50K volts. Each time it was because I relied on someone else to check/shut off master switches.
On the 480, back in the early 70's I was fixing a personnel hoist. The main disconnect was around the other side of the building. The hoist operator said he would go shut it off. He disappeared around the corner, about 10-15 minutes later he came back around. I stuck the screwdriver in the panel and was promptly kick across the safety enclosure. Turns out the operator went around the corner, started jabber jawing with someone and "forgot" to turn the power off.
The 50K zap I got is a whole 'nuther story. Lets just say I never take anyone's word about electricity anymore. I check it myself.