Battery Cutoff Switch

[SCFFR]

Just to add a little more security to my MkIV, I'm thinking about adding a simple battery switch in the trunk (have a FF Metal battery box) so was looking at the Summit and Jegs catalogs last night for battery switches. They all seem pretty much the same except for the amp rating. The basic switch is rated at 125A while the heavier duty ones are 300A with a momentary capacity of 1000A.
Since I will be using an Optima Red Top battery, do/should I go with the heavy duty switch or is the basic one sufficient. Electrical systems are definitely not my strong point. I assume that is the battery has 800CCA, the switch should be able to handle that many amps?

Many thanks,

Ron

[skullandbones]

A lot of this stuff is theoretical until you have an issue and then it's real enough for you. What I mean is you won't immunize yourself from electrical problems by over building it. I believe in a balanced system and one that fits your needs. My 302 is pretty middle of the road, I think. If you build to a certain amp rating the whole system should have that capability. So the lowest rated component in your system will be the weak point (e.g. wire size). I used to use "0" welding cables for a rear battery mounted hot rod. And I still had corrosion issues and the like. The point is the 125 amp switch will probably be OK. I got mine at NAPA and seemed to be built well. If you find any hot spots in your system when you are exercising it, you will see what I mean such as a hot cable or fitting that is hot to the touch. I also ran ground cable all the way to the battery and grounded the heck out of the system. In EFI, that is particularly important according to Ford Racing. Good luck on your build, WEK.

[avgjoe]

Don't go cheap! There are many el-cheapo battery switches out there that are only reliable as a paper weight and that's only on a calm day indoors. I presuume you wnat to be able to remove the "key" for a little added security.

I would go with one like this: https://www.pegasusautoracing.com/productdetails4.asp?utm_expid=10520551-6&RecID=1464&utm_referrer=https%3A%2F%2Fwww.pegasusautoracing.c om%2Fproductselection.asp%3FProduct%3D4435

or if not looking for a "key": https://www.pegasusautoracing.com/productdetails4.asp?utm_expid=10520551-6&RecID=10194&utm_referrer=https%3A%2F%2Fwww.pegasusautoracing.c om%2Fgroup.asp%3FGroupID%3DSWITCHBATT

If you do go cheap then make up a jumper to go around the switch when (not if) it fails.

If you're running EFI you should run a fused wire directly from the Batt to the ecm KAM (Keep Alive Memeory) pin so the ecm dosen't hve to relearn everything it was supposed to remember before the battery was disconnected.

Just because the the marketing dept says the Batt will put out x amps doesn't mean that the starter will use that many amps. The more accurate (at least closer) parameter to be concerened with would be the alt output, IMO.

[emac]

I added a secret cutoff behind the dash mounted to the firewall, it is the style with the removable key. I figured it would be easy to get to when leaving the car. Honestly, I never use it because the clock is a pain to reset, and I am anal about having the clock right!

I think it is a good feature for working on the electrical system or if you live in an area where you are concerned with theft.

[Avalanche325]

I did a battery cutoff. I ran a seperate fused circuit just for the clock.

[SCFFR]

Thanks guys.

Decided on the Moroso heavy duty unit (175 continuous/1,000 surge) which is NHRA, IHRA and SCCA approved. The price is $43 through Summit which is isn't too bad. I definitely was not going with the $20 plastic unit.

Like many of you, probably won't use it too much but better to have it and not need it than the other was around. I will install it in the trunk once I get the body off and send it to the painter. I wired the clutch safety switch to a push button under the dash which will be my main theft deterrent.

Ron

[SCFFR]

Thanks guys.

Decided on the Moroso heavy duty unit (175 continuous/1,000 surge) which is NHRA, IHRA and SCCA approved. The price is $43 through Summit which is isn't too bad. I definitely was not going with the $20 plastic unit.

Like many of you, probably won't use it too much but better to have it and not need it than the other way around. It doesn't have a removable key but since I'm going to put it in the trunk, it will be out of sight and I can keep the trunk locked. I wired the clutch safety switch to a push button under the dash which will be my main theft deterrent.

Ron

[edwardb]

Some may not agree, but the main purpose of the battery cut-off switch is safety, not security. Depending on the kind of event you're in, they're required and some rules require accessible from the cockpit including driver or from outside the car. Certain indoor car shows (like ISCA) require a battery cut-off switch or the battery physically disconnected (a pain). FWIW.

On my Mk3, the battery cut-off switch is in the trunk, and I have a lock out switch for the MSD module hidden under the dash that I can use if I want to disable the car. For my Mk4, I'm going to put the cut-off switch in the cockpit, but that's mainly because I'm using a front mounted battery. But from what I've heard, if someone really wants to steal one of these, likely they're going to winch it onto a car hauler, so whether it starts or not isn't an issue and maybe not a deterrent.

Personally, I would use the clutch safety switch for it's intended purpose, e.g. on the clutch pedal. For me anyway I just don't trust myself since my other DD's are automatics, and it's just too easy to jump in and hit the ignition switch. The potential safety hazard and damage from cranking while in gear, even if it didn't start, is enough for me to have the clutch safety working as designed.

[stang_killer]

I have a cutoff and to address the clock and other items that need power I have a jumper with a 5 amp circuit breaker, handles the devices but will trip if youtry to start car without the battery cutout on.

[Blue MK3]

I agree with edwardb in that the main purpose of a cut-off switch is for safety and to eliminate parasitic drain, not for security. My car is "primitive,", with no clock, EFI memory, etc., so I don't have any issues after I disconnect the battery. My cut-off switch consists of a disconnect device. It's a knurled plastic knob that when unscrewed easily removes the positive cable from the battery terminal. I don't know the brand, but when disconnected, there's no power to anything and no chance for a leak down. The battery is located just behind the front X-member in the engine compartment. It's probably as convenient as a switch in the trunk and is simple, foolproof, and probably inexpensive. Anyone trying to jump start a Cobra would have to know a lot to steal mine. Dealing with the ignition, then figuring out how to unlatch the hood and find and figure out the disconnect device would have to be pretty slick.

[SCFFR]

Thanks again for the information and feedback. My MkIV will also be very simple with no clock or really any electronic devices or accessories so not concerned about any "memory " issues. Everyone is absolutely correct that if someone wants your car bad enough, they will get it regardless of what you do but that is what insurance is for.
Since I will have easy access to the trunk when I remove the body and send it off for painting, will go ahead and install the cutoff switch then. Probably will use it infrequently but will be nice to have now and then.
On to the next project.
Ron

[emac]

I have seen several posts where people mounted the cutoff switch in the vertical panel of the trunk (over to one side). I ran a hookup for my battery tender into the trunk. How about some pics of your car so far!

[Blue MK3]

I would think the switch should be located as close to the battery as possible (for maximum isolation), so a trunk mounted switch makes sense if the battery is located there.

[Mesa Mike]

During my build (in 2001) I did the same. That is, put a battery cutoff switch in the trunk for security. I felt I could always lock the trunk. Last month I removed it and put in on the back of the car so track officials could turn off the switch in an emergency. I have been posting and reading on the various Cobra websites for 13 years. In that time there was a report of 1 Cobra being stolen. Not worth the time and effort, MHO.

[DVANSLEEN]

I bought the Pegasus HD model mounted in the cockpit. On cut off, it grounds the alternator through a resistor and breaks the ign. coil power. Without these features, you can't shut off a running motor with the standard cut off switches. (like a stuck throttle or such) I also feel better disconnecting all power when parking in my attached garage. Don't want my house to burn down!

[Pierre B]

I used a red paddle Hella cutoff switch, mounted to the firewall just above the transmission tunnel on my MKII. The paddle is attached to a lanyard that has the ignition key at the other end. The two pieces (paddle & key) always travel together. To keep the memory circuit alive, along with parking lights etc, I have a 5 amp self-resetting breaker across the cutoff switch terminals. That breaker allows enough current flow for minor circuits, but it positively willnot permit the engine to start. The breaker comes from NAPA.

[Arch]

I used a Ron Francis remote cutoff switch on the dash. Primarily as a safety item but is also one more layer to go through to start the car. It has worked well for 15,000 miles and because it is easy and accessible, I use it all the time.

http://i268.photobucket.com/albums/jj7/McQ2013/Withlables.jpg

Arch

[Pastenseverb]

I used a Ron Francis remote cutoff switch on the dash. Primarily as a safety item but is also one more layer to go through to start the car. It has worked well for 15,000 miles and because it is easy and accessible, I use it all the time.

http://i268.photobucket.com/albums/jj7/McQ2013/Withlables.jpg

Arch

Nice switches Arch. Where did you find them?
D

[SCFFR]

Doug,

I'm sure Arch will reply but I'm pretty sure the switches are from Ron Francis. I used them on my 1967 MGB GT restomod.
Check the Ron Francis website.
Ron

[Real time recon]

I added a secret cutoff behind the dash mounted to the firewall, it is the style with the removable key. I figured it would be easy to get to when leaving the car. Honestly, I never use it because the clock is a pain to reset, and I am anal about having the clock right!

I think it is a good feature for working on the electrical system or if you live in an area where you are concerned with theft.

Thats where mine is mounted,good location.