How to wire a 4 poll kill switch

chrisp · 02:01 AM

I purchased a four pole electrical kill switch from Longacre. What's the best way to wire it? I've read that the alternator needs to be killed at the same time.

I am assuming the battery wire goes to the large diameter poles and the alternator to the small poles. Where can I find the correct wire for the alternator (color)? Do I just cut it and mount either end to the two smaller poles on the 4-pole switch?

Thanks for the help.

Dantilla · 02-24-2006, 06:40 PM

It didn't come with wiring directions?
I did mine a couple of years ago, and don't remember for sure. The car is not at home so I can't go look for you.

I do remember that I did something wrong. The first time I pulled the switch, the car kept running. Oops! A quick scratch of the head, one wire moved, and all was well.

rattlsnak · rattlsnak's Garage

You dont have to cut the Alt. if you find another way to shut the car of instantly, that will work fine. Some people run the DME relay power side through it. I ran my coil power feed wire. As soon as you pull the switch the car quits. Either way, there is no way for the Alt to back feed and keep the car running because you are taking away its source to run.

Sigurd · 02-25-2006, 09:26 AM

How does the switch with the small connectors work? If it goes of with the large connector, I would use it to cut the current somewhere in the ignition system. Otherwise, the engine would not stop when you turned the switch off; the alternator produces electricity for the ignition so the engine would continue to run.

If the small connectors goes on when you turn the switch, I would connect one side of the switch to somewhere you have current from the alternator when the car is running. The other side I would have connected to a resistor or other power consumer such as a light bulb. This way, when the system is made powerless, with the engine, and alternator, still making RPMs, the alternator is not completely disconnected but has somewhere to deliver power to. You have to connect the ignition system to a relay so the engine stops when you turn the switch off.

rattlsnak · rattlsnak's Garage

Everything on 'side one' of the switch gets disconnected from 'side two' when turned. Hence, what I wrote above.

Early_S_Man · 02-25-2006, 06:43 PM

The small connectors are for ground and the alternator B+ 'hot' lead and there is an internal resistor to bleed energy built up in the stator windings when the power to the engine is cut. Large 'break' contacts to battery ... small 'make' contacts to load [bleed] the B+ energy so a large inductive HV spike doesn't occur ... which can blow out the rectifier diodes!

Zeke · 02-25-2006, 06:52 PM

My questionn has always been, what happens to the "energy built up in the stator windings" when the normal ignition key is turned off?

I know my 914 emergency cutoff switch had only the 2 poles at first and the engine kept running w/o a battery. Now, the electronic stuff is perhaps different, but the older coil powered ignition just kept on truckin'. Gotta cut thy alt circut, too.

chrisp · 02-25-2006, 07:05 PM

so is 6-pole mandatory or can 4-pole be wired to work properly?

rattlsnak · rattlsnak's Garage

You wont have an alt issue if you cut the ignition source. Its no different than turning of the ignition key. Some people cut the fuel source, but the car will still run for a few seconds (or more), and that will cause damage.

I have never seen a 4 pole cut off switch that makes contact on any of the poles when switched, BUT that certainly means then, that they are out there!!

Need to find out which one you have first.

Put an ohm meter across the terminals and try it both ways, and see which one yours is.

304065 · 02-26-2006, 12:40 PM

Why do you say you won't have an issue? The alternator doesn't stop charging when you cut the ignition and remove the battery. The remaining current in the alternator will create a gigantic spike in the second or so it takes for the engine to die.

roadside kill switch install help??

rattlsnak · rattlsnak's Garage

How do you turn off your everyday street car?

You turn off the ignition.

I understand what you are saying, and I think it was more of an issue on the earlier cars, but most of the racers around here dont bother with the alt portion anymore. Dave at TRE said they dont do them either.

My last three cars were wired without them, and after 'multiple' tet pulls, I have never had a problem.

Also, the one in the link is a 6 pole, i think he said he had a four pole.?

chrisp · 01:03 PM

.

chrisp · 02-26-2006, 01:01 PM

Yup it's a four pole by Longacre. In researching this more I noticed this is the same switch Dart in Colorado installs in their race cars.

304065 · 02-26-2006, 01:35 PM

I understand what you are saying but I still don't recommend a four-pole switch, which is why I posted a link to the six-pole instructions.

When I turn off my everyday street car I don't remove the battery from the charging circuit at the same time. So the engine stops and the voltage drops. When you disconnect the battery at the same time, the alternator has no load on it, so the voltage spikes off the chart. This is not only not good for the VR and the alternator diodes, it's not good for the CDI or any other voltage-sensitive components. Head unit, video camera (if wired to the car's main bus), data acquisition system, etc. all at risk.

Ahh, but you say, I've shut off the ignition, so the alternator can't produce voltage in the brief moment between when the switch opens and the engine quits, right? Put it on a scope and try it. When you charge the ignition coil with a Kettering-ignition and you open the points, you've shut off the current to the coil, right? But the spark generated by the breakdown of the field is enough to fire the plug. Same basic principle happening in your electrical system. There is enough residual magnetism in the decaying rotor field to make this an issue.

The Longacre four-pole switch is more appropriate to a late model or other modified car that's probably not even using an alternator.

rattlsnak · rattlsnak's Garage

I totally agree with you in 'theory'.

I was telling him to wire the 4 pole.

But, ... Electrons actually flow from neagtive TO positive..

Dont they??

chrisp · 02-26-2006, 05:56 PM

Interesting info. Thanks guys. Best bet is to get a 6-pole.

JohnJL · 09-22-2009, 02:29 AM

But if you already have a spare 4-pole?

The Longacre site here specifically recommends it for use with alternators. Here's their wiring diagram with two wiring options for 1- or 2-wire installations. I guess ours would be 2-wire so would their diagram have us wiring the blue wire into the switch (I shudder to think how to then complete the finicky generator charge light and diode?)

Longacre wiring diagram

304065 · 09-25-2009, 05:42 AM

John, that diagram is not for Porsches.

The 1-wire alternators are for American Cars or Aftermarket single-wire alternators. They use an integral voltage regulator which energizes the field on start-up.

The 2- wire drawing shows interrupting the alternator FIELD, not the battery positive. If you kill the FIELD, you have shut off power to the rotor so it no longer induces a current in the stator, which shuts off alternator output. However, the battery positive terminal is still connected to the alternator, which means that as the voltage decays there's still a load on the alternator, no problems.

If your 911 was made before 1982 I suppose you could interrupt the field. After '82 the voltage regulators are internal so that is impossible.

Remember, what is prohibited is interrupting the battery positive lead when the alternator is still running.