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Discussion Starter #21
Hopefully the attachment works (I'm at work so I can't access any image hosting sites) so you can see my rough OEM diagram. In that setup, the power distribution block is powered by the battery and also the alternator. If you installed a kill switch between the battery and the power distribution block, the alternator would still power the distribution block if the switch was thrown with the engine running.

If I attach the alternator to the starter hot wire (which is already attached to the power distribution block), the alternator would still power the car (but not the battery) once the kill switch is de-energized. This would essentially configure the car as if it were OEM.
 

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The reason this is challenging, Josh is that there are two different classes of alternator and the wiring of a shut off switch needs to be different depending on the type of alternator used. In cars that are several decades old or in custom performance applications it is possible to find what is called a self exciting alternator. For simplicity in wiring when doing your own electrical system or transplanting an OEM electrical system, some guys like to dumb down the electrical wiring requirements. One of the things they do to achieve this is use what is called a self exciting alternator or more commonly a one wire alternator.

Th one wire alternator does not use an external power source to excite its field. With some internal, to the alternator, wiring modifications the alternator is capable of exciting its own field. this type of alternator is commonly referred to as self exciting or one wire. You will find them for sale at all the usual retail distribution points Jegs, Summit etc and also alternator rebuilders. To my knowledge it has been many decades since they were ever offered on an OEM vehicle. Unless you changed your alternator to a one wire alternator you do not have one.

If you did have one this is one way the shut off switch could be wired to work properly;

Self Exciting Diag.jpg

The installation illustrated above uses a double pole single throw switch. The "Positive Distribution Block" at the bottom of the photo is functionally the same as the distribution block in your drawing. There is a problem with this double pole switch wiring style that I'll speak to a bit later.

Again, unless you have intentionally had a self exciting alternator built for the car the drawing above is not the wiring diagram you want to use.

All modern alternators use an externally excited alternator field today and some of the newer ones use the vehicle's ECU to determine when to excite the alternator field - essentially turning it on and off as the vehicle requires. The on and off effect is designed to assist CAFE standards by reducing power demands on the engine during normal operation.

The diagram below will illustrate the correct kill switch wiring for an externally excited alternator;

External Excite.jpg

You will notice the warning in the lower pic that tells us the two smaller terminals have a 20 amp speed limit. That means in the upper pic that the hot wire from the alternator would probably damage the low power portion of the switch. My alternator is self exciting. When I wired mine the hot wire on the alternator went to the hot post on the starter and the starter cable went to the large battery positive stud on the shut off switch.

The small posts on the shut off switch are adequate to power the alternator field. However, if you want to be absolutely certain you will not blow out that circuit while driving and stop charging, then you could wire both the field exciting wire and the alternator hot post to the larger, high amperage battery positive output stud.

If I remember correctly I lifted these drawings from a Longacre document that came with my shut off switch. As long as you already have a shut off switch robust enough to handle the starter you don't need to buy another switch if yours doesn't not switch two circuits. Just wire one side of the switch to the battery positive and the other side to the distribution block and also the alternator field.

You might want to check a Ford wiring diagrams manual to see how Ford powers the alternator field wire. It may be done in the distribution block which would simplify your switch install. If the field is powered from the distribution block then placing the switch in the circuit to the distribution block is all that is required.

Ed
 

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Josh,

I use a circuit breaker. I run battery power directly to the circuit breaker then to the battery box mounted distribution block. These wires are all 1/0AWG. From the battery box mounted distro block i run a wire to the cutoff switch then straight to the engine bay mounted distribution block. I possibly could make a quick diagram iff interested. Caution that it may not be neat as yours if i do not have the time.

 

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Discussion Starter #24
Thank you for putting that up and explaining everything Ed. My kill switch is a two-post variant, so I have to do things a bit different than what you posted. My alternator is also OEM, and it is excited via the distribution block essentially (through the instrument cluster), so my field wire is de-energized by killing power to the OEM distribution block. On that same topic, I don't think it would matter (in terms of shutting off the car) if the alternator continued to put out power. If the power cannot reach the distribution block, nothing down stream of it would stand to benefit. If the fuel pump, coils, injectors, ecu, etc. don't have power, the car will not run.
 

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Discussion Starter #25
Josh,

I use a circuit breaker. I run battery power directly to the circuit breaker then to the battery box mounted distribution block. These wires are all 1/0AWG. From the battery box mounted distro block i run a wire to the cutoff switch then straight to the engine bay mounted distribution block. I possibly could make a quick diagram iff interested. Caution that it may not be neat as yours if i do not have the time.
That looks great Troy! I am going to do something similar to what you've got as well. I've got the parts sitting in the trunk (ABS plastic sheet, circuit breaker, fuse block, terminal block, 5 relays, and a SSR), but it would take me forever to make a diagram of it (I just use MSpaint). I've got a 250 amp mini fuse in right by the alternator already, but I will probably need another breaker on that same run close to the battery. As I progress with this, I will be sure to post photos.
 

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If your looking for a switchable circuit breaker this is what I use: https://www.bluesea.com/products/category/14/30/Circuit_Breakers/187-Series?Mounting=Surface_Mount

I purchased a pair of "high amp rated" scorpion breakers from one of the audio websites like sonicelectronix. As soon as I received it I knew I couldn't use it. The terminals are wimpy and and the entire piece looks and feels cheap. They are guaranteed to cause problems. The Blue sea breakers on the other hand are top notch in my book.

It also makes for an excellent theft deterrent. If you don't know the breaker is there youll never get power and it makes cutting power to the car tool free. I mounted the breaker between the battery box and the cars sheet metal so its out of site. I just know where it is at and can slide my hand on the side and switch the lever.
 

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Discussion Starter #27

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Josh, and anyone else trying to wire one of these gizmos, I erred once again!

If you run the field wire to the battery positive terminal on a single pole switch it will prevent the car from being started. However, it will not shut off a running engine using a regular (non-self exciting) alternator. The reason it will not shut off the running engine is the alternator hot post and the field wire meet. When the engine is running the alternator power will be more than sufficient to energize its field windings and an attempt to shut off the car by breaking the circuit at the battery with the shut off switch will fail. It will behave similar to removing the positive battery cable from the battery and watching your engine continue to run.

In order for the shutdown event to succeed the alternator field circuit must be broken separate from and independent of the alternator's output. Unless it is isolated in the OEM power distribution block (which it might be but, I sort of doubt that) wiring both the field and the alternator hot post to the vehicle side of a shutoff switch will energize the alternator field winding and provide power to prevent the engine from shutting down.

The genesis of the double pole single throw switch in the diagrams in post 22 is to create two independent circuits one to power to the alternator field windings and one for the alternator main power out that is used to charge the battery. By keeping them separate and making / breaking them independently it is possible to either energize or de-energize the alternator. The de-energizing event will positively shut down both the alternator and also the engine.

If the wiring harness finds any way to get 12V to the alternator field winding it will be impossible to shut down the alternator and therefore the engine by using the shut off switch.

Apologies for the confusion. I did not intend have this play out in such a befuddled fashion.


Ed
 

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Discussion Starter #29
I am going to upload a few diagrams here and explain my understanding of each, starting with how my car is wired:


Anything that is red is powered with the key on. Obviously, if the engine is running, current will flow from the alternator charge post. If the engine is off, but the key is on, voltage will flow from the battery to the alternator. I acknowledge that my two post kill switch cannot shut that off. I would need a kill switch with two outputs to get remedy that.

This next one is my car with the kill switch in the "OFF" position. Again, anything red would be energized, and anything black is de-energized. You can see how I understand this to work in this photo:


As you can see, using the kill switch removes 12v input from the power distribution block. This would kill power to the entire car with the exception of what is left in red. If power is removed, the car has to die. At this point, the field wire would also lose power.

The only thing I can see (and I think I'm beginning to understand Ed here), is that power might sneak through that field wire on the alternator side. That field wire (small) would leak power into that distribution box and essentially keeping the car running until it melts.
 

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... The only thing I can see (and I think I'm beginning to understand Ed here), is that power might sneak through that field wire on the alternator side. That field wire (small) would leak power into that distribution box and essentially keeping the car running until it melts.
That is my suspicion Josh. I suspect, but don't know with certainty, that the distribution box allows the circuit that powers the field and the circuit that charges the rest of the system to merge inside the distribution box.

The easy way to test it is wire it up and see if the kill switch shuts off a running engine. If it doesn't then you need either a second switch for the field power or double pole single throw switch to handle both circuits in a single switch. If my memory is correct my drawings were from Longacre and at one time they offered just such a switch for just this reason.

I just did a search and Longacre did not show it but Fastronics did. They offer the two pole single throw kill switch to do just what we have been talking about. It is their part number 303-002. Here is the link => Kill Switch.

Ed
 

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That is a very nice unit, y2k. Allstar makes two versions of their switch. One is their part# ALL80158 and the other is their part# ALL80159. The 158 part# is the single pole switch and the 159 part# is the double pole switch. For non-self exciting alternators (what most of us have) the part#ALL80159 part is the one you want to get. BTW the one your link points to at Summit is the correct two pole unit for use with non-self exciting alternators.

Something worthy to keep in mind for anyone installing one of these is that, the Allstar Kill Switch is rated at 125 amps continuous duty which will work well with our standard output OEM alternators. If you have upgraded to one of the 200 or 300 amp aftermarket alternators, the kill switch will need to be upgraded to take the new higher continuous amperage that the hot rod alternator is capable of. Much the same as the story for upgrading the alternator hot wire when you go to the big units.


Ed
 

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Ed/Josh,


I understand what Ed is saying now. I have been running it this way during 2017 but have not driven the car much. Needless to say I am embarrassed to say that I have not even tried to use the cutoff to see what will happen if triggered. I have a bit of work going on right now so the blower is removed. I am hoping to get some stuff from the powder coaters tomorrow (Friday). If that happens and i can get it put back together over the weekend I will test it out as I have my setup routed just as you have it posted Josh, besides me using the additional circuit breaker and junction block. My deadline is Monday afternoon, after that I am out of the picture for a bit. Fingers crossed.
 

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Some times in tech at the track they will have me start my car. Then they test the switch.
 

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Discussion Starter #35
I am going to upload a few diagrams here and explain my understanding of each, starting with how my car is wired:


Anything that is red is powered with the key on. Obviously, if the engine is running, current will flow from the alternator charge post. If the engine is off, but the key is on, voltage will flow from the battery to the alternator. I acknowledge that my two post kill switch cannot shut that off. I would need a kill switch with two outputs to get remedy that.

This next one is my car with the kill switch in the "OFF" position. Again, anything red would be energized, and anything black is de-energized. You can see how I understand this to work in this photo:


As you can see, using the kill switch removes 12v input from the power distribution block. This would kill power to the entire car with the exception of what is left in red. If power is removed, the car has to die. At this point, the field wire would also lose power.

The only thing I can see (and I think I'm beginning to understand Ed here), is that power might sneak through that field wire on the alternator side. That field wire (small) would leak power into that distribution box and essentially keeping the car running until it melts.
I'm about 3 years late for the party, but I finally remembered to test this configuration for the battery kill switch and it works. It will indeed shut down a running engine and also prevents it from starting with the kill switch in the "off" position.
 

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Not a big deal Josh :).

Thanks for the feedback proving the switch wiring worked as you intended. It will help others who wrestle with the same issue.


Ed
 
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