Battery Cut Switch- what kind, how/where to install?

So after some playing around with things, I ended up deciding that moving the Rampage's battery was the more efficient thing to do as it avoided my having to fabricate a complicated new tray for it with the intercooler/intake piping that interfered with the stock tray. It's now safely tucked away behind the passenger seat in a HF ammo box- but I know that for the Challenge it needs to have a cut switch since it's been relocated. What kind of switch do people typically use? How/where do you install them so they make sense? Most that I've seen do not look like they're conducive to easily install onto a normal-bodied car...

could you make use of the radio antennae hole in the front fender for the cutoff switch? That would reduced the body panel hacking.

Since it's a Rampage with an open truck bed, you can probably just do one in the rear firewall above the battery to minimize the extra wire run associated with the switch. It's still accessible from the outside so i would guess it could conform to whatever rules are in place for external battery cutoffs, but don't take my word for it. Might have to have some sticker on the body or rear windshield pointing to it since it wouldn't be super obvious it was there. 

In reply to Vigo :

Putting it on the front wall of the bed is where I figured it would work best, but wasn't sure if that would work the best with there looking to be several layers of sheet metal there to go through, especially with a cutout like the cheaper switches (like this one) would requite.

Keep in mind, there are two types of battery disconnects, two post and four post.  Two post just shuts off main cable before it gets to anything, but if your car is running and you shut the switch, alternator keeps car running.  A four post has the main cable on two posts and the alternator charge cable on the other.  Shut that one off and car stops running.  Four posts are required for racing.  Two posts just keep the car from being stolen or allowing your battery to drain down over long periods of storage.

Is the battery allowed to be in the passenger compartment?

Stampie said:

Is the battery allowed to be in the passenger compartment?

NHRA rule:

8.1 BATTERIES 

All batteries must be securely mounted and may not be relocated into the driver or passenger compartments. Rear firewall of .024-inch (.6 mm) steel or .032-inch (.8 mm) aluminum (including package tray) required when battery is re-located in trunk. In lieu of rear firewall, battery may be located in a sealed .024-inch (.6 mm) or .032-inch (.8 mm) aluminum, or FIA accepted poly box. If sealed box is used in lieu of rear firewall, box may not be used to secure battery, and must be vented outside of body. Strapping tape prohibited. A maximum of two automobile batteries, or 150 pounds (68 kg) combined maximum weight (unless otherwise specified in Class Requirements) is permitted. Metal battery hold-down straps mandatory. Hold-down bolts must be minimum 3/8-inch (9.53 mm) if battery is relocated from stock and other than stock hold-downs are used ("J" hooks prohibited or must have open end welded shut.).

grm has said the rule on kill switch location is relaxed for cars running slower than 11.50 in the challenge supreme court thread, which I believe is now spelled out in the rules section of grmchallenge.com but i’m not sure your harbor freight ammo can is going to pass muster unless it’s metal.  I can help you with a cheap(ie pay for shipping because i get them free) metal ammo can that would be sufficient, but you still need to vent to the exterior and have separate hold down for the battery.  In a rampage the easier thing would be stick it in the bed with no need for a box.  Also remember the kill switch has to kill all operating so you need to run the alternator wire to the battery side of the switch or you’ll keep running after the switch is thrown off.

Ah, good old.. rules.

Thanks for posting that, it at least clarifies which specific type and size of hoops must be jumped.

tr8todd, my vintage race car has a 2 post switch if you wire the alternator up correctly the 2 post switch will cut everything. 

Also the car has two switches. One on the front fender near the cowl and another inside the car so you can kill everything while belted in. 

I bought a 4-post switch for my V8 Firefly but was having a hard time making it work (it just kept running). Currently it's wired as a two-post, with the alternator output wire going directly to the battery.  Everything else comes off the disconnect switch.  Could have saved money and bought the two-poster.  And yes, it's an EFI engine too.

My CRX race car came with a 4-post battery switch. It was mounted under the hood, but had a cable, with a loop handle, that exited at the base of the windshield. Of course, it had a proper "OFF" label next to the loop. Worked well for the 10+ years I had it. 

SkinnyG said:

I bought a 4-post switch for my V8 Firefly but was having a hard time making it work (it just kept running). Currently it's wired as a two-post, with the alternator output wire going directly to the battery.  Everything else comes off the disconnect switch.  Could have saved money and bought the two-poster.  And yes, it's an EFI engine too.

^Agreed on doing it this way.  If you get one that has also has W and Z terminals, it gives you further protection.  When the main circuit is interrupted, the W terminal closes and is wired from the accessory/ECU/etc side of the switch to ground, through a fat resistor.  This is easier on your electronics, mainly the voltage regulator in the alternator.  

I think the 4430 is the classic racecar kill switch.  It's been in every car I've raced, anyway.  

Pegasus 4430

I bought a 4-post switch for my V8 Firefly but was having a hard time making it work (it just kept running).

Mostly unrelated but i remember working on a hot rod (totally rewired from factory, would have been a 6 volt car originally) that wouldn't turn off with the key because the still-spinning electric cooling fan (which was wired to be on whenever the ignition was on)  would generate (literally) enough voltage to energize the coil of the main ignition relay and keep the rest of the car running. Just another funny anecdote about it sometimes being more complicated to turn the car off than one might think..

Four post is best, but don't run the alternator output through the small terminals.  Way over the rated load.  Efi cars are easy.  Find the trigger wire for the main relay and run that wire across the small terminals.  Main lugs lose the battery, small terminals shut off the injectors, etc.  It is probably safer to hook the alternator output to the battery so it is isolated from the electronics.  Voltage spikes when the battery goes out of the circuit  but the alternator is still spinning can cause troubles.

I ended up putting the battery back in the stock location after some trimming of the original battery try to make it fit with the new intake & IC piping... wiring and putting the cut switch in was juts going to be too much of a hassle for what little benefit would have been gained by moving the battery.

Moving the battery is easy, but making it "worst case scenario proof-ish according to XYZ's insurance's underwriter's CYA policy handbook" can be something else entirely. But, since most racing happens on other people's property, dem's the rules. 

Tom1200 said:

tr8todd, my vintage race car has a 2 post switch if you wire the alternator up correctly the 2 post switch will cut everything. 

Also the car has two switches. One on the front fender near the cowl and another inside the car so you can kill everything while belted in. 

Hey, yeah, so I'm trying to figure out how to install a switch in the Audi right now. I bought a two-post switch, because that was the obvious thing to do, and then I learned all this stuff about the alternator a.) running the car after you flip the switch and b.) dying a horrible voltage-spike-induced alternator-death because you shut off the circuit while it's still spinning.

But on my car, there are two leads coming off the battery, and one of them just goes to the starter and alternator. The other goes to the cabin to power the ECU and everything else. I tested the thing by disconnecting that ECU lead while the car was running. It stopped running. Right away. Am I missing something? Can I just use a two-post switch and wire that circuit through it, and be done with it, or am I somehow damaging the alternator by doing this?

Sorry for bumping a long-dead thread, but it seemed a better alternative to starting a new one all over again.

Some people wire the switch to open the ground side (ie: project Binky for one) Any reason this wouldn't work, or is there a reason to wire it to the hot side (ie: alt will keep the engine running)

MiniDave said:

Some people wire the switch to open the ground side (ie: project Binky for one) Any reason this wouldn't work, or is there a reason to wire it to the hot side (ie: alt will keep the engine running)

It seems like it would work. It would be no harder for me to wire it. But I'm not well-versed on this aspect of the electrical system. I'm not sure which of the two would be "better" either.

tr8todd said:

Keep in mind, there are two types of battery disconnects, two post and four post.  Two post just shuts off main cable before it gets to anything, but if your car is running and you shut the switch, alternator keeps car running.  A four post has the main cable on two posts and the alternator charge cable on the other.  Shut that one off and car stops running.  Four posts are required for racing.  Two posts just keep the car from being stolen or allowing your battery to drain down over long periods of storage.

IIRC (because I needed to find this out too) you run your ignition switch through the other two terminals.  This way the car shuts off just like you turned the key or flipped the main ignition switch.