Solve the battery disconnect switch wiring dilema once and for all!

[lqmustang]

Originally Posted by NiteRida

Question/clarification needed regarding, "cut the two factory charge wires at the alternator plug and tape them together, then splice in a wire at the plug and run it directly (after passing it through a fuse) back to the switch as drawn in Evil1's diagram"

Shouldn't you also trace these charge wires back to the hot side of the starter solenoid and take them off of it?

Just making sure. I'm about to do this to mine. Currently my switch is "only" on the positive side of the battery.

I'm in the same situation. I would think you should at least disconnect the original charge wire from the solenoid, otherwise you'll have a hot wire flopping around. BTW, after unwrapping the wires to where the 2 splice into 1, what a scary looking setup!!

[NotchAbove]

I have mine hooked up as below:

1) Positive side of the battery to one side of the starter solenoid. The other side of the solenoid goes to the cutoff switch. On the other side of the cutoff switch it attaches to all the other wires that were on the other side of the starter solenoid before hand.

2) Then where those wires used to attach to the solenoid you will find the wire that comes from the alternator. (This is the 2 wires that go into 1, at the starter solenoid it is only 1 wire.) This is the charge wire. You must run this back to the battery so the residual power is transferred back into the system. This wire runs to the positive side of the starter solenoid.

Throy: When you turn the car off, the power to the computer and everything else is stopped. The alternator has some residual charge that must go somewhere, and you don't want it going back thru the car into the computer system, etc. So you run the charge wire back to the positive side of the battery so it can charge it.

I have been running this like this for a few months, and it works perfectly.

[Mattstang65]

Just clip the two black/orange wires off of the plug and tape them up. Don't trace them all the way back and remove them, it's not neccesary and I believe they still serve a purpose. I've been running mine this way for over 3 years without problem. I followed a writeup by Smith Monte, but can't seem to find it right now.

[Mattstang65]

Here it is:

http://www.geocities.com/smithmonte/...ade.htm?200712

[hotrodder]

Originally Posted by EVIL1

Wired mine like this today, but with a 150amp circut breaker rather than a fuse. Works like a champ!

[gtconv91]

got a nice wiring diagram that i can email... if anyone wants it...

[hossracing]

If you have the heavy cutoff switch with the extra terminals for the altenator kill, couldn't you just run the exiter wire through it to kill the altenator.

Why, because you could run a 12 to the back instead of a 2 with a 175a fuse. Then still hook your alt. charge to the st. solenoid.

??

[virgil]

does 94 and up cars get wired different

[hotrodder]

I'll probably get bashed for this but, I ran 4ga. instead of 2ga. through a 150amp circut breaker. There is a dozen posts if you search saying that 4ga. is plenty big enough.

[dy85merc]

i just finished relocating my battery in the back with a cutoff switch,i used the diagram that EVIL1 posted and it worked perfectly.thanks a lot for the help.race on.

[nzane1980]

that diagram you guys are passing around isn't nhra legal it leaves the hot battery terminal hooked to the alternator all the time its called a battery disconnect switch for a reason it disconnects the battery from everything on the car you need the switch with the two small terminal and the exciter wire which turns the alternator on runs thru the smal contacts and the big set cuts the main hot wire in half not trying to knock anyone down but if i wreck it catches on fire i want my crap to be right so i live to see my kids and race again

[buffhomer]

The diagram came from me originally and I can assure you it is definitely 100% without a doubt NHRA legal. I have had it checked and approved by more than 1 NHRA inspector, and it was originally made to utilize the simple 2 post Summit battery cutoff switch (which is also NHRA legal). It will cut off the original power source (battery) and the running power source (alternator). Some people have other ideas about this or that and backfeeding mumbo jumbo and all, when IMO simple works best. Never had a problem and hundreds of other Corralers have never had problems with it either when wired in this manner with solid connections and clean grounds.

Feel free to wire it how you choose, as long as it works according to the rules then you're good. If you want to go above and beyond then by all means do it. No one can keep you from making your car as safe as your personal standards demand.

Here is the original diagram, along with the ultra-simple one I made for a 3G alternator conversion. Monte Smith helped out on this years ago when I first did it. BTW, for whoever asked, yes, SN95 cars would be wired a tad different.

[Blk88GT]

Mine is wired up as the diagram above. It works and passes tech.

I will be changing it to have one fuse/circuit breaker by the battery and one by the alternator.

Thanks for the tip, I never thought about adding a second one to isolate the wire.

[nzane1980]

guess they and you failed to notice the hot wire still energizes from the battery to the alternator yes your setup kills the car as in it stops running but that big wire with fire on it if it gets pinched in a crash can cause a fire the correct switch is sold by summit and others its only 60 something dollars but its up to who ever is in the drivers seat if your comfortable with it i say its fine i just didn't know if anyone noticed it was still hot is all. I 'm sure everybody goes for the other switch because its 16.95 lol but its really for cars that run without an alternator but hey sometimes like now budgets are tight and we just wanna race i get it

[Mattstang65]

after some thought, I've modified my wiring and fuse protection slightly on my 3G setup. It's still basically the same as the Buffhomer diagram, except that I've added a fuse next to the battery to better protect all the circuitry.

My reasoning is that the original fuse in the setup should be placed as close to the alt as posible, to protect from an internal alternator short or regulator failure. The fuse I added is to protect everything else, such as if there were a direct short (cut, pinched wire) in any other area of the main feed/charge wiring. I've added the "second" fuse (next to the battery) to the diagram so you can see what I'm talking about.




It's been mentioned that this setup "may" not be NHRA legal because it still leaves a "hot" wire energized going up to the alternator. Although the charge wire is still hot, when the switch is turned off all power is cut off that allows the engine to run, that's all the rules specify, nothing about the charge wire. The 4-post switch with alternator cutoff was mentioned, have you read the instructions? The post to the alt is a small lug that is for 10 gauge wire and specifys "20amp MAX". With todays vehicles having electric fuel pumps, fans, high output ignitions, etc.., alternator output easily exceeds "20 MAX amps" to maintain battery charge. With this particular switch, a high amp relay would have to be utilized, using the 10 gauge wire from the "cutoff" switch to energize the relay. Click on picture below and "open link" for full size.

[Brians93notch]

ackstang, where did you get the battery cable and ends that are shown in your pictures>?

[big vinny]

you dont want to have your alternator wire switched because if some one shuts kill switch off while car is running alternator voltage will spike and could damadge your ingition box or other electronics.

[dy85merc]

i believe the rule says you have to cut power from the positive side of your charging system. i wonder if there is a way to stop a voltage spike, because mine is like the diagram.

[buffhomer]

Originally Posted by nzane1980

guess they and you failed to notice the hot wire still energizes from the battery to the alternator yes your setup kills the car as in it stops running but that big wire with fire on it if it gets pinched in a crash can cause a fire

As I said, it is legal, it is correct to the letter of the rulebook. If you wanna go above and beyond then go for it.

I like the dual fuse setup on the alternator charge like someone mentioned. As for the voltage spike, there's a million different ways to go about that. I've used cutoffs dozens of times on various cars and never had a problem with a spike hurting anything. I don't think it's luck really.

[nzane1980]

mattstang65 20amps is plenty to run the exciter wire on the alt. its usually green with a red stripe on fords and it has a small current draw it basically tells the alt. wether you have the car running or not you run this small wire through those 20 amp contacts and the hot battery cable through the big terminals and thats it super easy hope this helps zane

[Mattstang65]

I did realize that, the way you stated your post was it needed to cut the power on the large charge wire (red in the diagram) when the cutoff switch is turned off. Your exciter wire theory is flawed. The way the diagram is drawn, when the switch is turned off, all power is killed to the starter solenoid, where most everything gets power from including the "exciter wire", and the motor does stop running. Motor not running = alt not turning and not producing. True, there is voltage on the red wire after the switch is "off", but with it fused near the alt and with the second fuse near the battery, it is perfectly safe.

[nzane1980]

no it's not, if you break the main battery cable its disconnected if you break the exciter wire the alternator cannot and will not charge to keep the car running. Do some research, I am giving you facts because i know the exciter wire powers the electromagnet in the alternator no magnet no power output and the whole car is disconnected from the hot battery cable and the alt can't charge so it can't run and that is the proper why to wire it. I have wired many complete cars to lighten them for racing purposes. I am only tring to help as this way is actually simpler and really probably cheaper, the correct switch costs more but you don't the 2 gauge wire and all those fuses . You actually leave the charge wire alone were the factory put it the main battery lead will disconnect it from the battery with the exciter wire being unhooked the charge wire isn't charging and therefore it can't backfeed and keep the car running. This way way unhooks every wirre from the battery its safe and simple you only have to run a 12 gauge back to switch and back to the alt and the hot battery cable to the large part of the switch maybe this makes it clearer er

[Mattstang65]

If your talking about not running the "dedicated" large charge cable (red wire in diagram) from the alt back to the battery, and only relying on the "factory" charge wire that's hooked to the starter solenoid, then yes your method needs to cut the exciter wire. That's not my prefered method, don't care if you agree or like it, both will pass "tech".

[dy85merc]

is it legal to run the wiring under the carpet or does it have to be underneath the car?i also agree with mattstang65, if it passes tech, it's all good. the fuse near the battery will cut all power to the alt. if there is a short.

[nzane1980]

well matt aparently you didn't read the thread title i didn't really care if anybody liked the way i and hundreds of others do it someone wanted to know the correct way and here it is your way might slip by in tech in but if you bet someone at a real race and they put up the money you won't be the winner anymore because the rule says battery disconnect and if that 2 gauge wire is hard wired to the battery it isn't disconnected i do not and will not care any excuse you give its still hooked up period point the end

[dy85merc]

the rules say disconnect the positive side of charging system. like the thread says "battery disconnect" is not legal. if you only disconnect the battery the car is still going to run. no matter what you do, there will always be a hot wire from the battery, unless you mount your switch right on the post. chill out dude. no big deal. period.

[nzane1980]

dude i'm gellin you know like that dumb commercial its all good i'm tossin back refreshing beverages i just like a good disscussion now and then i don't get no worrys racing is fun

[dy85merc]

it's all good. we all just want to race. if i make it through tech i'm doing good, race on.

[Mattstang65]

Originally Posted by nzane1980

well matt aparently you didn't read the thread title i didn't really care if anybody liked the way i and hundreds of others do it someone wanted to know the correct way and here it is your way might slip by in tech in but if you bet someone at a real race and they put up the money you won't be the winner anymore because the rule says battery disconnect and if that 2 gauge wire is hard wired to the battery it isn't disconnected i do not and will not care any excuse you give its still hooked up period point the end

Well I guess I'm NOT wrong after all. I've become sick of this hear say BS and the I'm right your wrong with out anything to back it up crap. I sent an email to Bob Blackwell , the NHRA general rules commitee CHAIRMAN, with a copy of the master cutoff diagram in question. He sent a prompt reply shown below.


---- Bob Blackwell <BBlackwell@nhra.com> wrote:
> Hello Matt,
>
> The way you have it in the diagram is fine, yes that wire would still
> have voltage when the master cutoff switch is in the off position, but
> it will meet the rule. Let me know if you have any other questions.
>
> Thanks,
>
> Bob
>
> -----Original Message-----
>
> Sent: Tuesday, March 03, 2009 6:58 PM
> To: Bob Blackwell
> Cc: > Subject: Master cutoff question
>
> Would it be possible for you to clarify if a particular master cutoff
> wiring diagram is acceptable? To myself and many others, the
> description in the rule book is too open ended and open for
> interpretation. I have attached a copy of the diagram in question.
> Please note, in the diagram, the red 2GA wire from the alternator is
> attached to the charging "output" lug and to the battery + side of the
> cutoff switch. Although there is still battery voltage present on the
> red charge wire after the switch is turned off, all voltage and
> "function" is stopped. When the switch is turned off the engine stops
> running. I look forward to your reply. Thank you.
>

nzane1980, if you want to further argue the legality of the the diagram you were bashing, contact Mr. Blackwell (his email is listed above).

I did not say that any other methods listed in this post are incorrect, only that there is more than one way to do the job. Hopefully we can put this thing to rest.

[nzane1980]

well still guess you can't read in my above post i said it cool if you (however it wasn't you but someone else) felt safe using it i was only pointing out the large 2 gauge wire is still hot and could pose a danger in event of a crash hopefully you me or anyone else needs it as i don,t wan't anyone to crash i'm just overly safe is all if the tech in will let you run and your cool with it then its all good man i aint got no beef with you relax go run and have fun

[dy85merc]

here it is

[kargola]

now I need to get mine done.

[Quik5oh]

Is there a summary now on how to do this the safest way possible?

[virgil]

[

Here is the original diagram, along with the ultra-simple one I made for a 3G alternator conversion. Monte Smith helped out on this years ago when I first did it. BTW, for whoever asked, yes, SN95 cars would be wired a tad different.


[/QUOTE]

do you know how the sn95 cars get wired thanks

[eighty8gtfiveo]

thanks for the diagrams! getting ready to do this in the very near future!