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I have looked over some of the older posts about the Battery switches. Seems like everyone puts the switch on the positive lead. I am looking at my MSD 6AL2 installation instructions and I warns against disconnection of the Positive First!
That's what's got me a little confused. "WARNING: During installation, disconnect the battery cables. When disconnecting the battery always remove the Negative cable first and install it last."- Straight from the manual.
I have moved my battery into my smugglers box in my 72 El Camino. Everything works fine, but I am looking into a disconnect switch for a few reasons. The vehicle wont see the strip much if any, but I want to 'hide' a disconnect behind the passenger seat if possible. It would make the cables going to the battery very short.
It seems 'conventional' to remove the NEGATIVE side of the battery first when working on electrical. Any thoughts??
 

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Discussion Starter #3
I get that! IF you are removing a battery, that makes all the sense in the world. But what about a disconnect switch? + or -
 

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I get that! IF you are removing a battery, that makes all the sense in the world. But what about a disconnect switch? + or -
It wouldn't matter, disconnecting either battery cable stops all current flow.
positive cable, if you interrupt the negative there still power flowing to the positive side. A short to ground could cause the circuit to still be live even with the switch turned off.
Nope, see above, disconnecting either battery cable stops all current flow.
 

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I just aint that bright. Splain it to me...... If I remove the Pos. or the Neg. Battery cable from my 1970 Chevelle,,, Where on my 1970 Chevelles do I attach a 12 Volt test light ( it has a Gator clip for ground and a sharp needle type pin that you would touch to complete the D.C. circuit) and " LIGHT UP " the bulb in the clear plastic handle?
I do know late model cars have capacitors for air bags and such, They will supply voltage even if the battery is broken or removed, untill they discharge.
I am very old and willing to learn new ideas. I just need to know how I can get a 12 Volt signal at the horn relay ( or anywhere else) in a 100% stock 1970 Chevelle with the Pos. or the Neg. Batt. cable NOT attached to the 12 Batt. in the car. Explain this to me very slow, I am old and a bit slow!
Over the winter I had the A.G.M. Battery ground disconnected my one owner LS-5/M-22 El Camino, The AM/FM radio would not play and it would not start......:crying:
Bob
 

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You want it on the positive side. Here is why - you also need to have the alternator feed going to the positive side of the battery between the battery and the cut off switch so that when you flip the cut off switch both the battery and the alternator are cut off from the system and the car will shut off.

If you have the cut off switch on the negative side, and you disconnect the negative battery cable, the car will keep running using the alternator feed.

Agreed, pulling negative or positive is just fine if the car is off, and then everything is dead. But, on a running car, you also have to make sure you take out the alternator feed, and you aren't going to do that by just removing the battery negative connection.
 

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I have looked over some of the older posts about the Battery switches. Seems like everyone puts the switch on the positive lead. I am looking at my MSD 6AL2 installation instructions and I warns against disconnection of the Positive First!
That's what's got me a little confused. "WARNING: During installation, disconnect the battery cables. When disconnecting the battery always remove the Negative cable first and install it last."- Straight from the manual.
I have moved my battery into my smugglers box in my 72 El Camino. Everything works fine, but I am looking into a disconnect switch for a few reasons. The vehicle wont see the strip much if any, but I want to 'hide' a disconnect behind the passenger seat if possible. It would make the cables going to the battery very short.
It seems 'conventional' to remove the NEGATIVE side of the battery first when working on electrical. Any thoughts??
for YOUR purpose. putting the disconnect on the ground would suffice. But if you were racing the car, it would need to kill the positive, and by your own admission, you MAY race the car, so you should probably put the switch on the positive side.


My malibu's battery exploded one night, It was a sidepost MEGATRON interstate piece of garbage that the positive terminal inside the battery had broken loose inside, and spun hitting one of the plates internally. The guy that had stopped to help, asked if he could help me. I said YES. Just give me your battery to get my car started, and once the car started, I pulled his battery back out, taped up my positive connector, and drove my car home running on just the alternator. Today's newer cars, the battery is actually part of the circuit and is needed.. Older cars, not at all, just needs to start and as long as the alternator is turning, the car will still run.

On a side note, if your car was a full race car with no alternator, then killing the ground may kill the car still....
 

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You want it on the positive side. Here is why - you also need to have the alternator feed going to the positive side of the battery between the battery and the cut off switch so that when you flip the cut off switch both the battery and the alternator are cut off from the system and the car will shut off.

If you have the cut off switch on the negative side, and you disconnect the negative battery cable, the car will keep running using the alternator feed.

Agreed, pulling negative or positive is just fine if the car is off, and then everything is dead. But, on a running car, you also have to make sure you take out the alternator feed, and you aren't going to do that by just removing the battery negative connection.
So are you saying you think a car can run off of the alternator with no ground path to complete the circuit to the ignition system?
 

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Of course not, you need a complete circuit to keep the car running.

You do realize that once the car is started, the battery is no longer supplying power to the ignition circuit. You can remove it completely and the car will keep running. The alternator is now providing power to run the car's ignition and also charging the battery.

So, what I am saying is that you can run a car off the alternator if you disconnect the battery cable once the car is running. Either battery cable. Both battery cables. The battery itself. The car will still keep running.

I will use my car as an example. The circuit in this case goes from "alternator feed/charge wire -> ignition switch -> distributor -> engine block -> alternator". There is your circuit. No battery in the circuit anywhere.

If you don't cut the alternator feed/charge wire and keep the ignition switch on, the ignition circuit stays live and the car keeps running. By having the external battery cut off switch also cut the alternator feed/charge wire, you break the circuit and the car will shut off. You can't do that if the cut off switch is only connected to the negative battery cable. That is why positive is preferred, because you can loop the alternator feed/charge wire in before the cut off switch, and when you flip that switch, it breaks the loop and disconnects the battery.

So are you saying you think a car can run off of the alternator with no ground path to complete the circuit to the ignition system?
 
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Just to clear this up, there's two reasons and methods to disconnect a battery.

-Battery disconnect for storage.

-Kill switch for racing.

A battery kill switch disconnects the positive OR negative cable at the battery. This removes all battery power from the car's wiring when the car is stored. It's done after the engine is shut down. I have this on my car, I interrupt the negative cable from the battery to the frame.

A kill switch is for racing. At the track, if you crash, a track worker runs up to your car and hits the kill switch at the rear of the car. This shuts down a running engine and removes power from the car. This is normally done in the battery positive cable but putting the switch in the negative cable should produce the same result. If the car has a stock style alternator, the kill switch needs a second set of contacts that interrupts the alternator's field feed wire. Not doing this will allow the alternator to continue making power and the engine will continue to run. There's an NHRA rule for this. Two pole kill switches are available for this purpose.
 

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Of course not, you need a complete circuit to keep the car running.

You do realize that once the car is started, the battery is no longer supplying power to the ignition circuit. You can remove it completely and the car will keep running. The alternator is now providing power to run the car's ignition and also charging the battery.

So, what I am saying is that you can run a car off the alternator if you disconnect the battery cable once the car is running. Either battery cable. Both battery cables. The battery itself. The car will still keep running.

I will use my car as an example. The circuit in this case goes from "alternator feed/charge wire -> ignition switch -> distributor -> engine block -> alternator". There is your circuit. No battery in the circuit anywhere.

If you don't cut the alternator feed/charge wire and keep the ignition switch on, the ignition circuit stays live and the car keeps running. By having the external battery cut off switch also cut the alternator feed/charge wire, you break the circuit and the car will shut off. You can't do that if the cut off switch is only connected to the negative battery cable. That is why positive is preferred, because you can loop the alternator feed/charge wire in before the cut off switch, and when you flip that switch, it breaks the loop and disconnects the battery.
Well, who would'a thunk it?

I knew you could disconnect the positive battery cable with the motor running but didn't realize it would keep running with no ground.

I disconnected the battery with my car running years ago and the wild voltage burned up the points and both headlights.
 

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I have the Battery Cutoff Switch on the Neg Post of the Battery in the Trunk in my car that I Cruzin & Race at a NHRA Track
this was done for convince and based on advise from a NHRA Pro Dragster/Door Car Racer

 

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Heh... yeah, there can be nasty side effects sometimes of doing that. I don't recommend it at all. But, it does keep running...

Well, who would'a thunk it?

I knew you could disconnect the positive battery cable with the motor running but didn't realize it would keep running with no ground.

I disconnected the battery with my car running years ago and the wild voltage burned up the points and both headlights.
 

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Discussion Starter #18
Thanks for the input. It gave me some good ideas. I will be looking into a breaker as WHT/73 did as well. The idea of locating a NHRA Approved kill switch in the rear is not going to be easy. I'll look into that, but for now, I go with disconnecting the positive.
 

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Heh... yeah, there can be nasty side effects sometimes of doing that. I don't recommend it at all. But, it does keep running...

When I was in college (automotive service) we were told that if you run a car with the battery disconnected it was POSSIBLE for a surge of electricity to make the fuel tank sending unit glow or spark, causing a fuel tank explosion, and to NEVER NEVER NEVER test an alternator that way. I'm not sure if there have EVER been any cases of such a thing happening, but that is how we were instructed.
 

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So are you saying you think a car can run off of the alternator with no ground path to complete the circuit to the ignition system?
If your referring to the negative battery cable, then yes the car will run without it once its started. The ground path is the alternator housing bolted to the engine block at this point.

It does not matter electrically which side of the battery is disconnected first, its a safety suggestion to keep the wrench from shorting to a grounding point. If the negative is disconnected there is no way to complete a circuit from the battery and therefore no chance of spark.

A disconnect switch needs to disconnect both the battery and the alternator charge circuit so an engine will turn off when switched off.
 
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