I fabricated a kill switch for my 928

[wallstreet]

GTP
What wire gauge are you using? Any one know the wire equivalent of the flat cable? The round one is longer.

Originally Posted by dcrasta

Cant tell from the picture but is that wire sufficient ? Looks a little thin, but good idea..

[Alan in AZ]

Originally Posted by 924CarreraGTP

Do you guys like my kill switch? ...

Sorry its NOT a kill switch. Though it could kill some of your electronics if you try to use it that way.

It is a battery isolation switch, but I would not do it that way, keep the wire big (1/0), short ~3" and non-movable (e.g. not on tool panel). This is suitable for maintenance use, battery charging & security.

If you want a real racing kill switch - you need to rewire the whole car, and really it needs to be on the outside, or accessible by wire pull from the outside.

Alan

[Alan in AZ]

Originally Posted by Plexus928

A switch between the relay and the fuel pump is easier,smaller switch can be hidden anywhere close to the drivers seat. I use a gravity cut off switch from a bosch injection system , auto shut off if the car is in accident (or flips)
The reset button doubles as a security off switch.

I have a switch that cuts off the fuel pumps too - its on the Pod near my right hand - really easy to turn off - I use it just about every day.

Alan

[924CarreraGTP]

I have a fuel pump cutoff switch as well. My car is actually setup on a different hot wire with a switch, relay, and fuse to the fuel pump. The PO said the original wiring to the fuel pump was burned. I checked it and he was right. This is probably the sourch of my draw. Hence the turn off switch. So far the wiring job is pretty solid though I did rewire some of it with wires from another 928. This rear switch is just a test idea. I wouldn't kill this switch while the car is running or anything. It's just to make it easier to turn off the battery for wrenching and battery preservation. That way I don't have to move covers, carpet, tool panel and all.

[Alan in AZ]

Originally Posted by 924CarreraGTP

I have a fuel pump cutoff switch as well....

I suspect that everybody does...

So my point is - lets call it what is is in case anybody else gets the wrong idea about this - switching the battery out of circuit when the car is running is a VERY VERY BAD idea...

Alan

[924CarreraGTP]

I also got the battery isolation switch for free. So that might help explain my idea. I would go back and change the original thread name to Battery Isolation Switch but I can't edit that part. So I'll just look stupid.

[MPDano]

I guess I'm Old Skool as that's how I have always referenced this part as a Kill Switch. I do see your point Alan.

Here is an interesting description in a Hot Rod Mag:

Battery Kill Switch - Switched On

A Battery Kill Switch For Security And Safety

From the February, 2009 issue of Rod & Custom

By Kev Elliott

Battery Kill Switch

I have to credit reader John Fobian with the idea for this article, since he contacted me after reading our news item about Outta Sight's slick battery boxes. These come with what was described as a kill switch, though John quite rightly pointed out that there's a difference between a kill switch and a battery disconnect switch. So, what is the difference? A kill switch will shut down a running engine without damaging the alternator, while a master/disconnect switch may or may not kill the engine, its job being to isolate the battery from the rest of the electrical system while the engine is not running. However, this type of switch can damage the diodes in the alternator, as a high-voltage spike can be created when the switch is flipped. It should be wired with one terminal connected to the battery's positive terminal, and the other to the car's electrical system, with the alternator output connected directly to the battery positive.

A kill switch has six terminals, or more correctly, three pairs of terminals. The large pair connects one side of the switch to the battery and the other to the starter motor, a smaller pair will be for the ignition and fuse box feed, while the third pair will be for alternator surge protection.

Most of us have seen cheap master switches at swap meets, available for a few dollars. They're easy to identify since they only have two terminals compared to the six terminals on a kill switch, and so long as one is aware of their limitations, they can work effectively as a cheap security device. With the big red key removed, your car's electrical system is disabled, so long as a thief can't access the rear of the switch to jump the terminals, or doesn't possess his own big red key! However, these cheap switches won't have an amperage rating as high as a quality switch, which will typically be rated at 1,000-amp-or-more surge and 150-amp-or-more continuous flow.

According to the guys at Flaming River, a disconnect or kill switch can act as a choke point for engine performance, so it makes sense to choose one with as high an amperage rating as possible.

So, with safety and security in mind, we figured a quick look at what's available in both kill and master switches might be useful, as well as how to wire a kill switch into your electrical system. They may not be the most exciting product you'll purchase for your project, but you could well be thankful you fitted one, whether to save a battery from draining or to shut down an errant engine.

Read more: Battery Kill Switch - Rod And Custom Magazine

[Alan in AZ]

The battery switch shown is quite actually adequate for normal duty, I have a similar one installed differently. However if you want the best battery switch money can buy - look for one from Blue Sea Systems: HD-Series Battery Switches - PN - Blue Sea Systems These also come in 2 way changeover and AFD options. Superb quality and sealed for marine use.

In the end how you install it is much more important than what it is. Don't add a new weak link to your cars higest power circuit.

Alan

[924CarreraGTP]

Originally Posted by Alan in AZ

The battery switch shown is quite actually adequate for normal duty, I have a similar one installed differently. However if you want the best battery switch money can buy - look for one from Blue Sea Systems: HD-Series Battery Switches - PN - Blue Sea Systems These also come in 2 way changeover and AFD options. Superb quality and sealed for marine use.

In the end how you install it is much more important than what it is. Don't add a new weak link to your cars higest power circuit.

Alan

Alan, I thought about this. The Blue Sea part is not copper. I would try to keep the parts copper at least for heat conductivity. Also think about this. If you ran a pull cable to this switch it could be used for racing. As a kill switch attached to the battery it would be useful as such if you were racing the car and rolled it. After all if you roll a 928, the body is going to be toast anyway. So why worry about the electronics? It would be better to kill the whole system than it would to burn to death in the car. The catch to it is that you cannot turn the system off while the car is running without fear of burning the alternator or the Jetronic.
I've done some positively bent things to a 928s electronics and they still work. I've hooked 50 amp chargers to the front jumper station to start a car over 100 times. The Jetronic still works flawlessly. The 928 is a pretty robust old dog. If anything I wouldn't make a habit of using it as a kill switch unless the car is upside down.
I'm working on a different ground strap setup. This is just the test for it. I have an original 911 ground strap. It's short and braided. I may use it.

[Alan in AZ]

The HD switch I showed is a simply superb switch - its current rating is 600A continuous, 2750A for 10 sec cranking. There is nothing to worry about with this switch - excepts its cost and size. I have 2 of these - I actually consider them works of art, I don't say that about much electric hardware.

The studs are heavily plated copper and sized for up to 4/0 cable.

If you reimplement your switch don't use any wiring on the ground point side - fabricate a copper/brass or aluminum bracket so the switch bolts to the GP directly.
Make the bracket sized to ~2/0 AWG.

This is not a racing kill switch and would not pass a sanctioning body check.

The point is if you are in the car, unconscious and someone needs to kill the car a kill switch should work to stop the car AND disconnect all power. Yours will not stop the car if the engine is running, so won't kill power => useless.

Alan

See pics for a good implementation strategy:

[MPDano]

$62.95 for that little switch on eBay

Blue Sea Systems #3000 Heavy Duty ON-OFF battery switch (632085030001) | eBay

[Alan in AZ]

Originally Posted by MPDano

$62.95 for that little switch on eBay

Blue Sea Systems #3000 Heavy Duty ON-OFF battery switch (632085030001) | eBay

Like I said - its the "Rolls Royce" of switches - you wouldn't expect that to come cheap right?

Alan