When connecting and disconnecting the battery, does it matter if ground or + goes first.

Everytime I DC the battery to work on the car, I unhook the + lead. Always feel wierd about touching that big cable though. Let a wrench touch the + lead on the starter the other day and it damn near welded to the post, and I almost wet my pants.

Neg (-) first - no ground no spark

Hooking it back up - Pos (+) first......................

I could be wrong but I'm pretty sure you should always unhook the (-) first and here's why: If you unhook the (+) first, touching just about any part of the car with the (+) will cause a spark because the entire car is still all ground while the (-) is still connected. If you unhook the (-) first, the entire car is no longer grounded and a spark will only happen if (+) touches (-) on the battery itself.
True??


+ -

Well now that makes sense.

So its better to unhook both leads from the battery when working on the car? I have just been doing the +

Unhook the negative first. Only unhook the positive if you're positive you're taking it out of the car. Catchy?

Negative should be first off and last on. Make sense?

In a negative-ground car, having the negative disconnected 'safes' the battery.

OK, got it, but bear with me.

So instead of unhooking the + I should be unhooking the - ? (when working on the car)

Or do I remove both to be safe? If I leave the + connected, then isn't the big wire that runs back to the starter still hot?

think this way.... if you unplug the + terminal when working, and you drop a tool that touvhes the positive terminal and ANYWHERE on the body...you have a tool arc welded to the body.....

if you unplug the - and you drop a tool and it touches the body, nothing happens,..... unless you touch the pos and neg side of the bat,

QUOTE If I leave the + connected, then isn't the big wire that runs back to the starter still hot? QUOTE


No, the pos cable to the starter is no longer an issue if the NEG side is disc. from the battery. When NEG. is connected, the entire car becomes the negative post of the battery and that's why it's easy to short something while working.

Disconnect NEG. while working. In this way, it is only possible to have a short if you
short the two posts at the battery. This isolates the uninsulated car body and engine/
transmission from wrench happy "mechanics"

off - first

on + first

I strongly agree with neg first. I whitnessed an accident with gas leaking and horn stuck on. I argued with the fireman cutting the pos cable with bolt cutters to stop and cut the neg instead. I backed away as the idiot ignored me cutting the pos having a little trouble twisted it to cut through and sparked it to ground. The driver was out already and the car did not explode but I yelled at the guy with the bolt cutters and called his station to talk to fire marshal. I guess cause Im not a trained fireman like him I dont know crap about electricity, I did know enough to get away from that guy when he was cutting and sparking on that Pos battery wire.

thanks guys, I usually need things explained to me 3 or 4 times.

Yea now I'm more confused. I take the negative off 1st and then the positive.

Negative comes off first and on last in a negative ground car.

Positive ground cars (early 50's Fords, for example) would be just the opposite.

The idea is to eliminate the body of the car as a return path for the current.

firemen are good guys, but their brain capacity is washed away by their training. I used to be in Hazmat and some of their ideas were farther out than I am.

PS - Especially the ones that wear the starched white shirts, with medals and waxed down hair. The wax must cause brain rot.

I guess on a 914 this might be a problem, I wouldn't know because my battery is in my rear trunk. Everyone argues over this, or gets confused. If you disconnect the + then make sure you don't touch the + battery terminal to any metal on the car, which shouldn't be hard to do, since metal usually bounces when dropped. There are also arguments on the sparks igniting the hydrogen or whatever that the battery is emitting, same thing as smoking around batterys. When you reconnect + is has a bigger spark than -. Never seen a battery explode, never even met someone that has seen a battery explode.

The technician that I work under/with at the dealership since I am a student always has me disconnect +. I dunno if that is a Ford only thing, or what, but that is what he wants me to do, so I do it. Personally, it doesn't matter to me, as long as one side is disconnected.

It DOES matter, maybe not to you, but it should.

Metal (a wrench, let's say) will bounce when dropped unless it's busy welding itself to a metal part of the car because the battery wasn't properly disconnected.

Disconnecting the ground strap FIRST ( - on most cars) will then allow you to then remove the positive cable and, if your wrench happens to strike a part of the body while doing so, you won't be greeted with a shower of sparks and feel like an idiot, or worse.

Obviously, if the ground strap is not disconnected, and if you're trying to remove the other battery cable in a tight space, any body metal the wrench touches will remind you of the 4th of July.

Your technician should have told you this.

If either side of the battery is disconnected, there is no way to spark it. Unless you manage to drop a wrench on the positive terminal and it grounds out.

I have forgot to diconnect a battery a couple times before when changing starters, and I have yet to see a wrench get welded to anything. It gets hot, real hot. I have seen a couple people when changing oil filters tap the positive on the starter bolt too, once again, it sparks and gets hot, no welding. I am sure, under some circumstances it will happen though. I am just saying of all the times I have seen and heard, I have never had that happen.



Obviously how? If the positive is disconnected from the battery, and the ground is not, there is no current flow, therefore there will be no spark. You have to have a complete path from positive to negative to have current flow. So, if the positive is disconnected, you have an open in the circuit, no current flow. If I tap the positive wire on the starter to ground, and the battery is disconnected at +, then there will be no spark.

Unless I am missing something here...

Back up a step, this is all about how to disconnect the battery in the first place.

iiibdsiil I think this is the main reason to disconnect the (-) first. Can you honestly say that you have been removing the Pos (+) side before the neg (-) and have never touched the wrench to the body an sparks went flying. If so you are lucky.

I hope this helps. A little simplified but...

If either terminal (plus or minus) is disconnected from the battery then the battery will not discharge.

The entire car body, engine, transmission and half of each electrical component is connected to the negitive (on our 914s) by the ground. So if you touch the body and the negitive terminal then nothing. They are already "touching" by the ground straps.

If while removing the positive terminal first you touch almost anything, then you will be creating a short. A short occurs because almost everything is grounded to the negitive side of the battery. Sparks will fly. The wrench may weld to the whatever you are touching. If you have been charging the battery it could explode. DO NOT DO THIS.

Removing the GROUND wire, negitive on the 914, will prevent everything electrical from working. This is the safe condition.

ALWAYS DISCONNECT THE GROUND FIRST

Okay, I thought we were past that. My bad, sorry about that. I jumped ahead.



I need to buy a lotto ticket now. Lol. I haven't been fortunate enough yet, although I am sure it will happen Monday at work now that you jinxed me.

So a what's the first thing I want to do when I pull my engine????

disconnect the NEG on the battery.

I have personally seen a few things. 1. Batteries will and do explode 2. wedding rings conduct and have sufficient resistance to get hot. 3 wrenches are excellent conductors and thats why neg first.

I know someone that was working on a car and the battery exploded. The car he was working on was a 914. This was in 1978 and he still bears scars on his face from the accident. Disconnect neg. first. Always