Positive or negative
Thread Starter
Intermediate
Joined: Aug 2020
Posts: 33
Likes: 1
From: MI
Positive or negative
When disconnecting the battery on my 78 to work on anything electrical, does it matter whether I disconnect the positive or the negative terminal on the battery? If so, why the difference?
Burning Brakes
Joined: Mar 2013
Posts: 750
Likes: 180
From: Springfield Missouri
Always disconnect the "negative" first and connect it last. Even though you can get sparks from disconnecting either first there is a less likely to be a threath of battery explosion by disconnecting the negative first.
Melting Slicks
Joined: May 2002
Posts: 2,474
Likes: 755
From: Laporte, IN
If you accidentally touch your tool to ground disconnecting the positive first a direct short to ground. Which can cause the battery to explode plus start a fire , weld the tool to that surface, Electrocute your self among many other bad things. Disconnecting negative first would have zero effects if touching ground.
Is my vette stock?? HAHA
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From: Im not allowed to tell you
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It’s mainly for metal frame cars. Your battery isn’t going to explode if you take the wrong one off. If you touch the wrench to the metal frame/ fender of the car while you are disconnecting the positive you will weld it to the frame and burn your hand, Then maybe melt your battery. ITs unlikely because you can hook jumper cables to it and use a welding rod and weld with just the battery in emergency cases. It’s a good trail rescue technique if youre out in the desert four wheeling.
So always remove the negative first and replace it last. And you will get a spark anytime you connect either if you have a current draw on the system
You should also remove any jewelry, IE. a wedding ring. If you have your wrench in your hand with a ring on it and pinch the ring between the wrench and the fender you will burn your finger to the point of needing it removed. We had a Naval safety magazine back in the 80’s showing the results.....not pretty.
Its very unlikely but possible to reach the positive lug from the negative ;lug and vice versa. Just pay attention
So always remove the negative first and replace it last. And you will get a spark anytime you connect either if you have a current draw on the system
You should also remove any jewelry, IE. a wedding ring. If you have your wrench in your hand with a ring on it and pinch the ring between the wrench and the fender you will burn your finger to the point of needing it removed. We had a Naval safety magazine back in the 80’s showing the results.....not pretty.
Its very unlikely but possible to reach the positive lug from the negative ;lug and vice versa. Just pay attention
Last edited by Rescue Rogers; Aug 28, 2020 at 12:05 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,022
From: New Braunfels Texas
If you touch the wrench to the metal frame/ fender of the car while you are disconnecting the positive you will weld it to the frame and burn your hand, Then maybe melt your battery. Its unlikely because you can hook jumper cables to it and use a welding rod and weld with just the battery in emergency cases. It’s a good trail rescue technique if you're out in the desert four wheeling.
Jebby
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
I don't believe that anyone can "electrocute themselves" with 12 volt DC power............
I have a battery disconnect switch. I chose to install it on the Positive side, as I do not want power going ANYWHERE when the battery needs to be disconnected. Overkill? Maybe. But, it's my car....
I have a battery disconnect switch. I chose to install it on the Positive side, as I do not want power going ANYWHERE when the battery needs to be disconnected. Overkill? Maybe. But, it's my car....
Last edited by 7T1vette; Aug 28, 2020 at 01:47 PM.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,108
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
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I don't believe that anyone can "electrocute themselves" with 12 volt DC power............
I have a battery disconnect switch. I chose to install it on the Positive side, as I do not want power going ANYWHERE when the battery needs to be disconnected. Overkill? Maybe. But, it's my car....
I have a battery disconnect switch. I chose to install it on the Positive side, as I do not want power going ANYWHERE when the battery needs to be disconnected. Overkill? Maybe. But, it's my car....
You my friend are living a dangerous life thinking that......its not the voltage, its the amperage....small voltage a high amps will stop your heart and shock the **** out of you....High voltage at any amperage will go from a horrendous burn to just plain blowing you up....
Remember putting 9 volt batteries on your tongue to test if they were dead or just p;aim pranking your buddy....multiply that by 700 times and see what happens. I came up with that by estimating volume of a 9 volt vs a car battery Size.
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Joined: Jan 2006
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From: Crossville TN
OMG..... They live among us....... 
Let's do the math. Normal body resistance with dampened probes = 300,000 ohms. Voltage 12 volts DC
E(voltage) = I(current) x R(resistance) or I = E / R. 12 / 300,000 = 40 millionths of an amp from a 12 vdc battery...if YOU spit on and grabbed each terminal with each hand and squeezed hard to absorb as much current as you possibly could.
DC current required to stop a heart is in the range of 300-500 milli-amps, or 300-500 thousandths of an amp. Using the lower number of 300 milliamps, That number is about 7500 times the current received from a 12 volt battery. I don't think that I am too worried about getting contacted by 12 vdc.
Now, if you are wearing a metal ring and choose to work under the dash with the battery connected, your RING could cause a dead-short if it touches 12 vdc AND ground at the same time. It will draw LOTS of amps and experience induction heating to several hundred degrees in seconds....which will melt your flesh down to the bone in a few more seconds. So 12 vdc is not something to mess around with IF YOU HAVE METAL OBJECTS IN OR ON YOUR HANDS. So, please disconnect the battery before working on or around anything electrical on your car.
Let's do the math. Normal body resistance with dampened probes = 300,000 ohms. Voltage 12 volts DC
E(voltage) = I(current) x R(resistance) or I = E / R. 12 / 300,000 = 40 millionths of an amp from a 12 vdc battery...if YOU spit on and grabbed each terminal with each hand and squeezed hard to absorb as much current as you possibly could.
DC current required to stop a heart is in the range of 300-500 milli-amps, or 300-500 thousandths of an amp. Using the lower number of 300 milliamps, That number is about 7500 times the current received from a 12 volt battery. I don't think that I am too worried about getting contacted by 12 vdc.
Now, if you are wearing a metal ring and choose to work under the dash with the battery connected, your RING could cause a dead-short if it touches 12 vdc AND ground at the same time. It will draw LOTS of amps and experience induction heating to several hundred degrees in seconds....which will melt your flesh down to the bone in a few more seconds. So 12 vdc is not something to mess around with IF YOU HAVE METAL OBJECTS IN OR ON YOUR HANDS. So, please disconnect the battery before working on or around anything electrical on your car.
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
There are many good reasons that factory instructions for any but the most minor repairs begin with, "1. Remove the negative battery terminal."
With a little searching you'll find numerous threads about what happens when you omit that step! Working near the starter or alternator are the easiest places to make a direct short to ground. I don't recall serious injuries being mentioned but fusible links definitely melt...
With a little searching you'll find numerous threads about what happens when you omit that step! Working near the starter or alternator are the easiest places to make a direct short to ground. I don't recall serious injuries being mentioned but fusible links definitely melt...
