battery cut off switch...How to wire?

supercatxr7

Registered User
My battery is mounted in the trunk and I just picked up a Flaming River Battery cut off switch. What is the correct way to wire the switch to totally cut power on a 90 sc? I read an older post on the website, but of course there were 20 different ways of doing it and everybody was saying everybody else's way was wrong. Can someone tell me the correct wiring?
 
supercatxr7 said:
My battery is mounted in the trunk and I just picked up a Flaming River Battery cut off switch. What is the correct way to wire the switch to totally cut power on a 90 sc? I read an older post on the website, but of course there were 20 different ways of doing it and everybody was saying everybody else's way was wrong. Can someone tell me the correct wiring?

I think that was my post that you're referring too. I never did put my battery in the trunk because after that post I was more confused than when I posted it. I hope you figure out a way to do it. I'd like to know also. Good luck!
 
Here's how I did mine.

This is the battery position. Right Rear. It's a little cheezy right now. I'm planning a fabricating a stainless battery box soon. You don't have to enclose your battery but you can't use J-hooks for hold downs either.
 

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I cut away the bottom right side of the license plate bracket and trunk lid and attached the on/off plate. Then when I race I just take off the license plate. It doesn't matter which post you hook up power and ground to on the cut off switch. Next I will weld a piece of sheet metal to close off the hole, paint it, and clean up the area so it looks clean.
 

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Will you pass tech at the dragstrip using the style cut off switch that you have (as opposed to the "push off" switches)? Also, I thought you had to wire the switch to completely kill all power to the engine when turned "off", meaning you'd have to somehow cut the power from the alternator as well as the battery. I'm getting ready to install the trunk mounted battery in my 90 XR7, so I'm trying to get all the facts straight.

-Rod
 
As far as I know the rules are:
1. You must have rear mounted kill switch. Must label where the off position is.
2. You can't use j-bolts to hold the battery unless they are welded closed.
3. If your car has an open trunk you have to have a sealed battery box. Our cars don't so you don't need a sealed box although it is still a good idea.

I don't know about disabling the alternator but I don't think you need to.

I wouldn't pass tech because I have j-bolts holding down the battery right now. They let me race anyways on a one-time pass. Next time I must have 3/8 bolts holding the battery to the floor.

If anybody has any info on a alternator kill switch let me know.

BTW, anybody that plans on doing this; I wouldn't use anything less than 1 guage wire for the long stretch from the trunk to the engine compartment.
 
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Rod: here is a drawing of what you are talking about.You need the proper switch to cut off the battery and the alternator. www.moroso.com
Part #74102 for battery & alternator disconnect switch.
Part # 74105 T-handle push pull battery disconnect kit for switch.

Randy
 

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This is off the NHRA website.


"I have a street car that I occasionally run at the strip. I've relocated the battery to the rear. What else do I need?"

"Any car with a relocated battery must be equipped with a master electrical cutoff, capable of stopping all electrical functions including ignition (must shut the engine off, as well as fuel pumps, etc.). The switch must be located on the rear of the vehicle, with the "off" position clearly marked. If the switch is of a "push / pull" type, then "push" must be the motion that shuts off the switch, and plastic or "keyed" typed switches are prohibited. Also, the battery must be completely sealed from the driver and/or driver compartment. This means a metal bulkhead must separate the trunk from the driver compartment, or the battery must be located in a sealed, metal box constructed of minimum .024 inch steel or .032 inch aluminum, or in an NHRA accepted plastic box. In cars with a conventional trunk, metal can simply be installed behind the rear seat and under the package tray to effectively seal the battery off from the driver. In a hatchback type vehicle the battery box is usually the easiest solution, since the alternative is to fabricate a bulkhead which seals to the hatch when closed. At present, Moroso is the only company which offers an NHRA accepted plastic battery box, part number 74050"

I'll probably get the right switch eventually. Righ now I can pass tech at my local strip so I'm OK for now. Sounds like a sealed battery box is the best way to go as well. I don't know how picky the tech inspectors are at your local tracks but it is better to be safe. They are not too strict at my track. If you have something done wrong they will usually let you run as long as you fix the problem before you come back next time and it isn't a huge potential hazzard, like a leaking oil pan or something.
 
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I know that NHRA wants the cutoff switch in the positive, but wouldn't be better and easier to cut power to the ground? You cut power to the ground and NOTHING works, including the engine. Just thinking out loud.
 
None2Slow said:
I know that NHRA wants the cutoff switch in the positive, but wouldn't be better and easier to cut power to the ground?

No. That wouldn't kill the alternator.
 
It's a little bit unorthodox but I have mine so that the cutoff switch disconnects the battery ground. The way I make that work with the alternator is by having a constant on 80-120 amp selenoid that cuts off the alternator. Then the ground to from the selenoid (16 guage) goes back to the cutoff switch also. So when I flip the cutoff switch, it disconnects the battery ground, and the ground of the selenoid at the alternator so it disconnects the alternator also.

I just can't do things the normal way. It's a curse.
 
Randy N Connie said:
Rod: here is a drawing of what you are talking about.You need the proper switch to cut off the battery and the alternator. www.moroso.com
Part #74102 for battery & alternator disconnect switch.
Part # 74105 T-handle push pull battery disconnect kit for switch.

Randy

Randy,

Shouldn't I use something larger than 10 gauge wire from the alternator to the switch? I would think that wire would need to carry quite a bit more than 20 amps from the alternator to the switch.

What I'm planning on doing is running 1/0 gauge from the battery to the switch, and 1/0 gauge from the switch to the distribution block under the hood. The starter solenoid will be connected to the disribution block by 1/0 gauge wire. Then I will connect the alternator output to the switch with 2 or 4 gauge. Does this sound ok?

Thanks,
Rod
 
...

I agree on running larger wire from the alternator. I ended up using 1/0 gauge from the battery to the cut off switch and then to the starter relay on the drivers fender. I then ran 2 gauge from the alternator back to the battery. Works good so far. I am also putting in a 175 amp fuse between the alternator and battery.
 
You would definately want to run some heavy wire from the alternator back to the switch. That's why I decided to use the selenoid up by the alternator and just shutoff the ground side. That way I'm just running 14-16 guage wire from the alternator switch to the battery shutoff.

I was told that if you really knew what your doing, you could check out the wire diagram of all the wires in the plug that goes to the alternator and find one that would shut down the alternator. Ideally you could just run that wire back to the shutoff and avoid using a selenoid or running the main power cable all the way back to the shut off switch and forward again to the alternator.
 
Slysc said:
I was told that if you really knew what your doing, you could check out the wire diagram of all the wires in the plug that goes to the alternator and find one that would shut down the alternator. Ideally you could just run that wire back to the shutoff and avoid using a selenoid or running the main power cable all the way back to the shut off switch and forward again to the alternator.


I was really thinking about doing that. After making my own wiring harnesses for the past couple cars that I've put together, I don't think it would be too difficult to figure this out.

Thanks,
Rod
 
Instead of using a big *** relay to cut the alternator use a small ISO relay to cut power to the coil pack +. It's a whole lot easier and if your large solenoid goes they are harder to get on the road. You can buy an ISO relay anywhere.

Jeff
 
I posted what the manufacture recomended minimum wire size that
should be used with there switch.So you would use this size or larger.
I would go larger on the alternator,& 1 on the rest.

I would think that the manufactures minimun wire size is right.
And just that the minimun!

RANDY
 
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If you use the second pole on the cutoff switch and cut the power for the coil then you don't have to worry about running large gauge wire for the alternator, and have less wiring to deal with anyway. Don't make it so hard. this should have been a 4 post thread.

Jeff
 
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