Battery Cut-Off Question

[supercharged]

I have poured through the threads on this site and the video online dealing with battery cut-off or kill switches. Not anti-start switches but something that will quickly disconnect the battery from the trucks circuit.

I am planning this for two reasons: To keep the old wiring from draining my battery and to keep someone from stealing the truck - since it does not lock!

My question is this almost all of the threads and videos show the switch being placed off the positive post of the battery prior to the positive cable going to any other component. Why isn't the ground cables used for that instead.

It seems it would be just as effective, just as easy and possibly safer than messing with the positive line.

What am I missing?

[tincan1966]

They mainly interrupt the positive circuit because a short to ground to make something work is easier than trying to get alternate power.
Also- old wiring does not drain batteries, just because it is old- defective components drain batteries.

If I were to install something as you are wanting, considering the power to the ignition switch feeds from a wire off the horn relay, I would interrupt the circuit from the horn relay to the "BATT" side of the ignition switch. You can use lower amperage components and not have an obvious interrupt switch. This can be done with a remote wire off the battery post of the starter to a hidden switch- a simple "on-off" to trip a relay.

Just a suggestion.

[LostMy65]

@Tincan,
you mention a 'remote wire' - which I think you mean a wire in a hidden (remote) location.
But then I wondered if you meant a Remote Switch. It made me think if there is such a thing as a Switch that can be turned off or on by a Remote.
For example;
How about an inconspicuous switch connected inline to the coil - something that can be controlled by a key fob remote?

[LostMy65]

Here is a couple related threads;
.
http://67-72chevytrucks.com/vboard/s...light=security
.
and;
.
http://67-72chevytrucks.com/vboard/s...light=security

[tincan1966]

As with my own personal truck, I am using a negative output from my alarm system to trigger a relay that will interrupt the circuit from the horn relay to the ignition switch when I "arm" the alarm. My BATT power to the alarm is run separately from the starter, thru a fuse, to the alarm itself.

I am running a 6 channel alarm system, so I have several optional outputs I can use for various other functions.

But to answer your question, LostMy65, YES it can very well be controlled by a keyfob type system, such as a very basic 2 channel keyless entry, but utilizing the outputs for different functions. Most of these systems use a negative trigger output, and built in circuit protection and relays, making designing a system a lot easier.

[supercharged]

Originally Posted by tincan1966

They mainly interrupt the positive circuit because a short to ground to make something work is easier than trying to get alternate power.
Also- old wiring does not drain batteries, just because it is old- defective components drain batteries.

If I were to install something as you are wanting, considering the power to the ignition switch feeds from a wire off the horn relay, I would interrupt the circuit from the horn relay to the "BATT" side of the ignition switch. You can use lower amperage components and not have an obvious interrupt switch. This can be done with a remote wire off the battery post of the starter to a hidden switch- a simple "on-off" to trip a relay.

Just a suggestion.

But what ground?
If the battery is not connected to the chassis and engine block and you are sitting on four rubber insolators, there shoud be no ground.

[tincan1966]

All I am saying is that all the companies manufacturing cut outs have spent bunches of money doing it their way, by interrupting the positive cable. I just figure they know what they are doing. I have no reason to question their research and testing. I am sure it will work to some extent, any way you want to try it. I have no idea why, it's just the way everyone does it and no reason for me to challenge it.

You can do it any way you'd like, I merely offered a suggestion.

If I may ask, why are you so adamant about not installing it in the positive cable?

[contagious102]

They are made for racing, and to prevent fire in case of a wreck.Most race cars have electric fuel pumps and the best way to kill the pumps is on the positive side.If you have 12 volts still on the pump and have a wreck ,it may find a ground in the twisted metal of the car.

[vin63]

This is what I have to use on my race cars with a battery. I also run one on my truck since I moved the battery to the rear under the bed (and I've run my truck at a local 1/8-mile drag strip from time to time). My battery disconnect switch is presently mounted behind the rear bumper, but for a street vehicle you can mount one just about anywhere. There are plenty of wiring diagrams on the Internet for the switch that you end up using.

http://www.jerrybickel.com/batteries...-switch-1.html

[donthekawguy]

I have one on my truck under the hood. The PO raced the truck. If I leave it on the battery drains in about 4 hours. Its a PITA to have to lift the hood to turn it off and on.

[racecougar]

Originally Posted by supercharged

My question is this almost all of the threads and videos show the switch being placed off the positive post of the battery prior to the positive cable going to any other component. Why isn't the ground cables used for that instead.

Because these switches are typically installed to meet NHRA's rules, which state that the switch must interrupt the positive side, rather than the negative side of the circuit.

Originally Posted by donthekawguy

I have one on my truck under the hood. The PO raced the truck. If I leave it on the battery drains in about 4 hours. Its a PITA to have to lift the hood to turn it off and on.

On these trucks, it would be quite quick/easy to track down a parasitic drain using nothing more than a multi-meter.

[supercharged]

Originally Posted by tincan1966

All I am saying is that all the companies manufacturing cut outs have spent bunches of money doing it their way, by interrupting the positive cable. I just figure they know what they are doing. I have no reason to question their research and testing. I am sure it will work to some extent, any way you want to try it. I have no idea why, it's just the way everyone does it and no reason for me to challenge it.

You can do it any way you'd like, I merely offered a suggestion.

If I may ask, why are you so adamant about not installing it in the positive cable?

Because I thought I read somewhere that abruptly cutting the positive feed to the starter and coil could somehow cause them to go bad and also if you are messing with the positive lead and accidentally touch ground you have a fried battery. If you messing with the negative lead and touch ground no big deal.

And I am not looking to just cut power to the starter or engine I want to cut all power off - so when it sits for days there is not accidental drain on the battery.