Battery Disconnect , Positive or Negative ??

Should the battery disconnect switch be installed on the Pos. or Neg. side. Can you support your theory ?
Bob

 

I have mine on the positive side. If i remember right, that is how the NHRA rule book states it to be installed. You must also run your alternator feed between the battery and the switch so when its in the off posission it will kill the power to the hole car, including the engine. If you put the switch on the ground side of the battery the engine would continue to run, as it doesnt need battery ground.

 

Slayer is probably right on the racing rules, but I always use it on the ground (negative?) pole. When I'm not using a a disconnect, I always take off the ground cable from the battery. Long time ago I was told to do it this way, don't remember the reason now. This way, if you have a tool or other metal and it hits the positive post and another piece of metal on the car, there won't be any problem with shorting out since the there is no ground from the battery.

 

I have mine on the ground side in my Hot rod.

 

i asked this about 5 years back........great thread, I will see if I can dig it up.

 

The ground wire is the most sensible one to use, just like it's the first off a battery and the last on. When you connect or discounnect a battery with the ground attached, even a shut off switch, you take the risk of a spark arc. And we all know what that can cause. Nothin on the electrical system can or will work with a ground absent.

 

and to support this further, modern computerized cars typically switch the ground for the loads, rather than the hot or positive. Seems those ECU's/ECM's like to be grounded, so not only are they very well grounded, but they're switching the battery negative.
The above does not allow for NHRA's rulings.

Roger

 

I agree with you on the arcing, but if the engine is running, disconnecting the ground will do nothing. There will still be a chassie ground. The alternator will continue to supply power to the ignition and the accessories alowing the engine to run.The questiun I have is what are you using a disconnect switch for? Are you using it as a safety item or just to disconnect the battery when the car is not in use?

 

Thanks guys, lots of good advise.
I will be using the disconnect switch as a safety feature while the car is parked in my garage. I don't trust my elec. skills. I think I will go with breaking the ground. If I am wrong , please let me know.
Thanks again,
Bob

 

really OT but sometimes when i was workin on my 54 i would use the battery cables and battery like an arc welder and weld the Posts with the cables hahaha, yeah i know thats not safe or good for the battery

 

I know alot of newer cars have a tab on the ground side to hang up when you pull the terminal off. (If that makes any sense). So I would go with the Ground. Plus like dickster said if theres no ground there def no power.

 

I have mine on the negative cable, I use it when the car is parked to save the battery. But I also use it as a anti-theft switch, my switch has a key that is removable when it is turned off. If I park it anywhere I am worried about it I just take the key with me.



CBB

 

Mine in on the +. My support theory is that I've just changed the battery for the first time after 10 years in the car.

 

I have mine on the positive side also

 

I've got mine on the positive side. The reason is if you have a radio when the power is lost you loose all presets. If you cut the positive but run a small wire to the radio this doesn't happen. But if you loose ground there is no way to have any power

 

phat rat is right, that's the only way to maintain memory, although, if the stereo has a removable faceplate this is unnescesary, as the memory is stored in a chip. otherwise, IT DON'T MATTER!

 

Any Racing organization rules say it should be on the + side. That's where I run em. And i too agree with phat rat. you can kill main power while your accesories have a little juice.

 

My old truck isn't a racer so I have mine on the ground side. I had it on the hot side for a long time but kept burning out diodes in my Delcotron alternators. By the time I moved the switch to the ground side, I had a pile of Delcotrons to match any pile of skulls Gengis Khan ever left outside a conquered city. Havn't lost an alternator since I moved it. I notice the newer switches have an alternator terminal so this prpbably isn't an issue with them.

 

I have mine on the negative side as well, no reasoning behind it other than thats the way my dad who is a old rodder said to do it. Good thread.

 

It looks like there are many different opinions on this issue. So far the score is:

Disconnect the Pos. = 5
Disconnect the Neg. = 8
Doesn't matter = 3

Just to fine tune the question a bit, there are no electronics/memory issues, and no need to shut down a running car. The sole purpose is to store a vehicle safely & not worry about a fire hazard.

I have had the misfortune of having an unattended car catch fire on 2 occasions. These were unaltered vehicles with factory wiring.

Any more ideas???

 

Yep. Don't touch them electrics! LOL

Seriously, mine is on the negative side - I asked the same question on another forum and the consensus was for that side.

 

Does it really matter? If you disconnect either the positive or negative cable to the battery, isn't the circuit interupted, stopping any flow of electricity?

Having said that, I always have placed the disconnect on the negative cable.

 

Alright, since you're still checkin'...if you're going NHRA dragging, it must, as many others have said, be on the positive side. Done.

If it's just for storage safety, as you have said (and others use it), use the negative. Done.

The one thing I dislike about using the positive is that often the switch terminals are left exposed and ready to get touched by a wrench or something, causing a massive spark showering short. It's a little more work to keep them properly insulated.

Negative cable, no problem with this.

 

I never thought about that. Good point.

 

Damn, you guys have radios?

 

Shut off the positive-no juice running anywhere. Even diodes in an alternator can fail and create a gound which equals fire. This happened to a guy I know. My car/truck start right up even after long storage. Make sure rubber fuel lines, etc are in good condition.

 

Marine battery disconnect switches are intended for the positive side. Better quality ones have built-in terminals for the alternator wire that are separate from the battery cable terminals. When the switch is off, the alternator is de-energized too.

 

I can see reasons to do it both ways. Mine is on the ground side, but since I put a new clock in the car I have not been using the shutoff. You can run a small wire with a fuse to make up the difference on either side and the fuse will just pop if you try to start the car. Lots to think about actually...

 

NHRA rules mandate that a battery-disconnect switch be installed on the positive side of the battery.

This device is not intended to save your radio presets........

 

Is it just me that thinks this makes more sense than any other post here, If you kill the ground and not the positive, any dead short upstream will still be powered and could cause a fire, that can't be good whether riding, racing or stored, I'd say the closer to the + battery post the better too.