Battery Kill Switch Setup

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71 Nova
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Battery Kill Switch Setup

Postby 71 Nova » Fri Jan 19, 2007 10:25 pm

My Nova has the required kill switch for my trunk mounted battery (installed when I got the car). I got a suprise changing my alternator the other day, finding out that the wire from the battery to the alternator was still hot even with the kill switch in the "off" position! I found a wiring diagram which indicates that this is a normal setup. Is this type of setup (with the alt hot with the kill switch "off") legal for NHRA drag racing? How have you guys wired up your kill switches?
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trunkbat3.jpg
Battery Kill Switch Wiring Diagram

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Postby John_Heard » Sat Jan 20, 2007 7:31 am

Yup, that's normal.

That alternator charge wire has to be on the battery side of the kill switch to prevent it from powering the car when the kill switch is turned off. There's several things you could do if it makes you uncomfortable, such as putting a constant duty relay in line with the alternator charge wire so that when the main power is off it also breaks that circuit. Or perhaps you could put something else in line to make it easy to disconnect when you're working on the alternator, like a circuit breaker or fuse.

Since we're on the subject, I would like to add that I think it's a VERY good idea to put an additional kill switch in easy reach of the driver that is in series with the rear mounted kill switch. I want to stress that YOU CAN NOT COUNT ON TRACK PERSONNEL TO TURN THAT SWITCH OFF if you wreck or on fire. I have one mounted in my car in easy reach. You'll find that if you do put one in it is very handy also.

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Postby 71 Nova » Sat Jan 20, 2007 10:57 am

Great thanks. I don't have a problem with the alternator being powered all the time, I just didn't understand the kill switch wiring setup and got surprised when I took off the alt. That's a good idea to have a cockpit kill switch; I can see where that would be quite handy, with enhanced safety. Thanks for the info!

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Postby dadnova » Sat Jan 20, 2007 4:36 pm

Make sure you put it within reach with the belts on and tight as well. My son and I relocated our switches to the roll gage on the top front side, for when strapped in you can't reach the dash. We have four switches that have to all be on ( for theft reasons ) however a kill switch or power switch on the roll bar as well. So we can turn it off instantly if need be. Safety first.

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Postby jones_performance » Sat Jan 20, 2007 9:26 pm

what i am doing is i'm gonna use a cable to attach to the switch arm in the rear (my bropther cnc'd some nice switch arms for the switches) with a handle near the driver to activate the switch. will also come in handy for the time you get strapped in and realize you didnt turn the switch on and have to get unstraped and out etc.
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Postby sc racing » Sun Jan 21, 2007 9:16 am

Thats a great idea Kevin.How many times have we forgotten to turn the switch on....probably as many times I hit my head on the window net mount! I think I will have to steal your idea.

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Postby Wayne Carroll » Fri Jan 26, 2007 12:30 pm

Kill Switch.

They have 4 post kill switches, rather than the common 2 post. You will have the heavy posts for the positive break from the battery to all other systems in you car. But, you will also have smaller post for a positive break to the alternator field wire that will pass through the switch to the plus side of the battery through the 2 smaller posts.

The 4 post Kill Switch has a voltage sink to absorb the alternator voltage on shutoff so that it is not feeding back voltage to your systems or remains hot after shut off. NHRA does require ALL systems power to shutoff from a single switch.

Call Flaming River, or find it in the catalogs from Jeg's or Summit. If I recall correctly, Moroso also offers this 4 post type of switch for just this problem. It is one shut off and convenient.

I too, have the dash switch that I can also shutoff the whole car in an emergency or fire - that is always very good advice.

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Postby sc racing » Fri Jan 26, 2007 8:32 pm

I wired in a charging system sutdown relay from Painless Wiring so the feedback wont keep yhe car running it works fine.

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Postby 71 Nova » Mon Jan 29, 2007 8:46 pm

I guess I'm still a bit confused. If you wire up your kill switch and alternator as shown in the diagram above, I don't see how the alternator could keep any systems running since it is only connected to the battery when the kill switch is set to "off". That setup should be NHRA legal, correct???

Having said that, I like the idea of a four post kill switch to power down the entire vehicle's power systems. No suprises that way. Think I'm gonna get one.
Thanks all.

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Postby dadnova » Sun Feb 04, 2007 2:50 pm

Looking at your diagram closer your + lead from the battery does not go to the switch. My + goes to the switch so if its turned off everything is off period. Then + from the switch to a ford post where Alt. and everything else is wired to requiring + feed. Thats why the swich is not working properly.

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switch

Postby sixty_foot » Wed Feb 14, 2007 11:13 am

isnt the purpose of the master cutoff switch to disconnect the battery and shut off electrical components? the wiring diagram shown above, would still leave the main power feed to the solenoid hot. shouldnt this main wire be interrupted at the master switch also ??

s f

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Postby John_Heard » Fri May 23, 2008 1:36 pm

The main purpose is to shut the engine off, along with fuel pumps and other accessories, and that is the test that NHRA does when they look at how it functions. Must kill the engine when you throw the switch.

If you've got the starter solenoid in the trunk, it's only a short length of wire that is hot all the time. Problem is most of those disconnect switches are not rated for the current the starter needs.

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Postby stroker1 » Fri May 23, 2008 2:10 pm

dadnova wrote:Looking at your diagram closer your + lead from the battery does not go to the switch. My + goes to the switch so if its turned off everything is off period. Then + from the switch to a ford post where Alt. and everything else is wired to requiring + feed. Thats why the swich is not working properly.
I don't understand your description. If the alternator output is connected to the same place everything else is connected to, then you cannot shut down the car with the rear kill switch. The alternater will keep powering the circuits. RIGHT? :?
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Postby rustbucket » Fri May 23, 2008 6:11 pm

does everybody go through the trouble to suit up, strap in, window net, gloves helmet and hit the ignition? About the time you realize the master switch is still cut off, all of your crew has headed to the line and their out of screaming distance.
I do it every trip to the track. Sometimes twice. it really sux.lol
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Postby 79 Camaro » Fri May 23, 2008 10:21 pm

rustbucket wrote:does everybody go through the trouble to suit up, strap in, window net, gloves helmet and hit the ignition? About the time you realize the master switch is still cut off, all of your crew has headed to the line and their out of screaming distance.
I do it every trip to the track. Sometimes twice. it really sux.lol



LOL! Thats a good one!!! I do that at least once or twice a race!! :lol:
I hate that! :x HAHA!
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