crazeinc

Hey guys...I'm installing a rear mounted battery and I picked up a master disconnect to say NHRA legal, but I really am not sure what wires I should hook up to it. Can I just take the starter wire to the disconnect and then a wire from the disconnect to the battery? Or the same thing only with the ground wire?

I hope this doesn't need to be complicated because this thick wire is expensive as hell and I'm tired of working with it.

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1982 Camaro Z28

should be running 11's this spring...we'll see
Check the website for progress http://members.fbody.com/Pro82Z/

Engineboy

I don't think it matters..either one you "disconnect" with the switch will disarm the battery.

Anybody else??

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

Red Devil

I'm not sure what the rulebook says, but I'm going to say the negative. Since the electrical juice flows from there first, I'd guess that's where you'd want to kill it first.

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"Perfection is a trifle dull. It is not the least of life’s ironies that this, which we all aim at, is better not quite achieved."

-W. Somerset Maugham

The ODB

It definately needs to go on the positive cable.

ODB

lonsal

iTrader: (2)

It doesn't matter. I was always disconnecting my positive cable. But now it is too worn for my wrench. So I've started disconnecting the negative instead.

ede

it does matter, per the NHRA rule book the disconnect MUST be on the positive. i'd think that anyone that was wanting to comply with the rules would spend the 12 dollars and buy a rule book.

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ICON Motorsports

1st & 3rd

88 427 Camaro

Positive.

Also, you have to run the alternator to the battery side of the disconnect so the car kills when the master switch is turned off.

Miles

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88 427 Camaro
12.18 @ 113mph 1.75 60ft

www.koolmeister.com

Red Devil

Learn something new everyday I guess. Ok now, can anyone tell me why they want it set up like that? Is it b/c they also want the alt. neutralized?

Engineboy

Once again I will guess..(I don't follow drag racing and its rules.. )

I would imagine that its so if the car is wrecked and/or still running for some reason they can reach over and shut the whole thing down. Safety reasons.

Could you imagine being pounded into the guard rail with the car on its roof and still running/leaking gas/etc.??

This way they could disarm fuel pumps and ignition sources from the outside of the vehicle.

This is just a guess.

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

ede

good guess engineboy, main thing is to kill the fuel pump and disable the car if it's wrecked from the outside.

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ICON Motorsports

1st & 3rd

Engineboy

I knew that was what the switch did, I just didn't know if that was the reason they wanted it like that.

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

Red Devil

The reason for having it, I understand. What I'm confused on is why they specifically want the positive side disabled.

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"Perfection is a trifle dull. It is not the least of life’s ironies that this, which we all aim at, is better not quite achieved."

-W. Somerset Maugham

ede

they don't want a hot wire running through the car, most people wire in a ford selanoid so the wire is only hot when you press the starter button

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ICON Motorsports

1st & 3rd

Red Devil

Ok, I still don't get it. Electrical flow starts from the negative terminal, so why kill the positive side?

AlkyIROC

If the race is not raced, (why else put the battery in the rear), then it must pass the rules in the NHRA/IRHA rulebooks. The master switch must be connected to the positive side of the battery so that it disconnects all the power to the rest of the car. If it was on the negative side then there would still be positive electrons on the positive cable from the battery to the starter/fuel pump etc. However unlikely that the curcuit could be completed, the less chance of ot happening the better.

Disconnecting the battery must also kill the engine. The field wire from the alternator will keep the car running. If the engine keeps running when you disconnect the battery you'll need to install a relay to disconnect the field wire when the power is disconnected.

The kill switch must be mounted at the rear. It must be marked as what position is off. If it's set up as a push/pull style, push, is the off position. Switch must not be keyed or plastic. The push rod must be a minimum of 1/4".

All the rule requirements are in the rulebook. You don't have to buy a new rulebook every year since the rule changes from year to year are very tiny. They usually are wording changes or new rules to cover things that were never considered before. See if your local speed shop has last years copy. They'll usually sell it for less that the cover price.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

8Mike9

Depend if you're referring to conventional flow, or electron flow..and how you wer etaught I guess.

Hey, post this Q on the electrical board, I didn't pay much attention to the theory in class.

The ODB

He's saying since the current actually comes from the ground source in a car.
The current actually comes from the metal of the car body & drivetrain to feed electrical accessories. The negative battery cable completes the circuit to allow this to happen. Because of this, grounds are the most important wires/cables in a car.
The standard reason to cut the positive is because of the possibility of alternate ground paths forming in the event of an accident. If any sheetmetal or metal battery case comes in contact with the battery posts, then any short would be localized at the battery.

ODB

Red Devil

That is what I was looking for. Thanks!

crazeinc

Thanks for the info guys. I hooked it up to the positive cabling and seems to work fine, but haven't had the car running yet to see if it will indeed shut off the motor.

Hopefully, I'll get some pictures of it tonight.

JoelOl75

Heres a little tip for you that most tech inspectors will let slide, but if they don't you can remove in 2 seconds. I noticed you don't have a computer controlled car, but at least you won't have to reset your radio stations every time you kill the switch and us computer guys won't have to "relearn" our fuel/timing curves. Put a small <10 amps >5 amps circuit braker bypassing the master switch. You can use a fuse but if you have the switch 'off' and try to start it you will have to replace the fuse. A manual resetting braker from radio shack works good.

crazeinc

Sure enough the motor doesn't cut off when I flip the switch. Which alternator wire do I run to the disconnect to cut the motor and what gauge wire do I need?

AlkyIROC

I'll have to assume you use a 10SI style alternator (older style). There should be 3 wires not counting a ground strap. The main large power wire and 2 smaller wires going into a plug. The smaller red wire can be directly connected to the main power wire. The other wire (should be brown with a white stripe) is the field wire. That's the wire that needs to be disconnected. I have a schematic of how a relay needs to be wired in but it's very rough and unlabled. I'll see if I can make a better copy or some sort of jpg pic and post it later.

I did a quick search through some search engines and couldn't find anything telling how to do it. I guess it's up to me to get a picture made of the schematic.

If you have a newer CS style, non-rebuildable, alternator with more than 2 wires on the plug, you're on your own. The 10SI is a little bigger and heavier but at least you can rebuild it.

AlkyIROC

OK. Here's a basic pic of the shutdown curcuit. The wire marked red coming off the alternator is actually the brown wire with the white stripe. This pic assumes you have a one wire alternator. The wiring of the relay is up to you. Pins 86,87,30 and I think 87a depends on the type of relay you have. There should be a schematic of the relay on the side of it. The disconnect switch on mine is my actual master power switch on the dash. If you disconnect the battery at the rear with a kill switch it should still kill the engine since you are killing all the power but I haven't tested it yet to be sure. I don't see why it shouldn't. Those wires marked "red" and the wire from the battery should be at least 12 gauge.



[This message has been edited by Stephen 87 IROC (edited February 19, 2001).]

AlkyIROC

So did you get it figured out to shut the car off?

crazeinc

Honestly Stephen I've been so preoccupied (sp?) with other things this past weekend I never even got a chance. I did save your diagram and really appreciate the help. Hopefully sometime early this week I'll hook it up.

The ODB

the alternator kill is much easier if you
use an external regulator.