Thread: Master power switch. Electrical GURUS needed

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For nhra need kill switch on rearmost part of vehicle if the battery is relocated to the trunk

Originally Posted by Chev malibu

As to no master cutoff necessary, does this only apply to the VW, as to the ET/mph, or any car that runs slower then that? I'm sure there is some class, maybe street class (?)that runs without external cut off switches. Least I have never noticed them on the cars. They race, then drive home in them..If I ever take the Cobra to a strip, I hope I'd be in that class, and still drive it home after..

So would the manual "ignition off switch" that Denny mentions include the keyed ignition switch, after all that's manual?

A master cutoff switch mounted on the rearmost part of the car is required with any battery "relocation" or when the car dips into the nines or exceeds 135. On a Cobra, it's a matter of interpretation by the tech official. If the car was built as a turn-key by a professional builder, then it's hard to argue against the battery being in the "original location", no matter where it is in the car. A car built entirely by a home builder might be interpreted another way, but if a Cobra shows up at Firebird with a front-mounted battery that is secured well in the car and separated from the driver by a firewall, I'm gonna sign off his tech card and let him make passes. If the battery is in the back, secured well in the car and separated from the driver by a rear bulkhead or firewall, I'm gonna sign off his tech card and let him make passes. The tech inspector has to use a modicum of common sense in making these decisions. It all depends on safety. If the car will be safe for the driver, the guy in the other lane and spectators on-looking, then common sense says to let the car go make passes, regardless if it is exactly within the scope of the rulebook.

I'm not saying to skirt the rules, I'm just saying that if the battery in a Cobra is mounted in the rear, well secured and separated from the driver with a bulkhead, it could well be argued that the battery is in the "original location" for that specific vehicle and thus needs no rear mounted master cutoff switch until 9.99 or 135. Let common sense prevail.

As far as the other kill switch in the driver's compartment, it is separate and apart from the rear-mounted master cutoff switch. Here is the verbage from the 2009 NHRA Rulebook....
General Regulations, Section 8:3, Ignition.....
"Each car in competition must have a positive-action on/off switch, capable of de-energizing the entire ignition system, in good working order and located within easy reach of the driver. Momentary-contact switch prohibited. Magneto "kill-button" type switch prohibited."

Hey Chev Malibu,
I've been out of touch for a while so no response from me. I do know what a keep alive is and have extensive experience in this area.

Where I am coming from, is your keep alive will be feeding a ground to ALL Circuits via the low amperage fused line. Not just the few that you intended (i.e. radio), but rather everything. A keep alive is generally directly wired only to the items that need power to keep the memories active.

If you have the master switch wired to the ground and use a keep alive to supply a fused ground line you are essentially suppling ground to everything. If you forget to switch on your master and try to start the car, you will blow the fuse on the keep alive and your memory items won't have power in the future.

Sometimes we males of the species just have to get into a tussle, don't we? You all been out there scrappin', and I been sitting here in my corner watching, and common sense tells me I should just have another cuppa joe and keep shut, 'cause you're all on the right track, and sometimes, I listen. Carry on.

Originally Posted by MRJB1929

Hey Chev Malibu,
I've been out of touch for a while so no response from me. I do know what a keep alive is and have extensive experience in this area.

Where I am coming from, is your keep alive will be feeding a ground to ALL Circuits via the low amperage fused line. Not just the few that you intended (i.e. radio), but rather everything. A keep alive is generally directly wired only to the items that need power to keep the memories active.
That would probably be the ideal way to do it, and since at this point it is really only the computer memory that I need continuous power to, I may be able to fish a wire to it. As it would only be a ground wire, this may be far easier to do than a positive wire. I hate tapping into a computer wire in general, but the ground should not be a problem.

If you have the master switch wired to the ground and use a keep alive to supply a fused ground line you are essentially suppling ground to everything. If you forget to switch on your master and try to start the car, you will blow the fuse on the keep alive and your memory items won't have power in the future.

That is essentially what I would want to happen, for security reasons mainly. Other circuits would be fused, so if a short developed somewhere in the car, say while it was sitting in the garage, either the keep alive fuse, or the items own circuit fuse should blow..(I hope)..Would you agree?

Hi Chev Malibu,
I get your point as to what you are doing and logically it should work fine as a complete kill to the system.

Is there a possibility for a ground bleed through the computer? I run an LT1 with a computer (actually have two cars with LT1's) and I think there is the possibility of a bleed happening. It likely won't be a problem except on the inadvertant start-up that we discussed above... but as long as you are prepared for it, it shouldn't be a problem.
You mentioned "Splicing" into the computer but wouldn't it make more sense to ONLY suppling the ground via the Keep Alive?
Jerome

Originally Posted by MRJB1929

Hi Chev Malibu,
You mentioned "Splicing" into the computer but wouldn't it make more sense to ONLY suppling the ground via the Keep Alive?
Jerome

I'm not sure exactly what you mean? Do you mean, do not wire the computer ground directly to the keep alive, but allow it to be grounded via the frame, as it is currently, or did you mean wire the ground directly from the AL91, to the switch, rather than splice into the current ground wire?

I suppose this would be the only way that the switch would still act as a theft detterent, as the computer draw amps are so low, it wouldn't blow the keep alive fuse in a hot wire type situation. I could run a ground wire from the computer, directly to the battery side of the switch. That would maintain a circuit, even if the keep alive fuse blew.

Bingo, Now your cooking

After looking at the pros/cons, I decided that;

I will run a computer ground directly from the battery negative side of the switch, rather than going through a keep alive wire. This will allow me to still retain computer memory, with the switch turned off. I don't have/need a clock, so I can't really see the need for a keep alive any longer if I wire it this way. This then covers the problem of the keep alive fuse blowing, if I forget to turn on the master switch when starting. (I still plan on having the switch on the negative cable for ease of wiring it, also for working on the car).

I believe that in an emergency type situation, accident, smoke from under hood, electrical burning smell, etc., ones instinct would be to first switch off the ignition, secondly to turn off the master switch. This would also avoid the problem of wrecking the alternator.

The keyed master switch would be the first line of defense from thieves. You really don't leave a car like this unattended for to long in the first place, although I may have to make the odd "pit" stop, if you know what I mean.

As the master switch is possible to jump, if a thief really had the time, and intent, I think the addition of a hidden switch, on the tranny neutral safety switch wiring would be a benefit.

Sound reasonable to you guys?

Originally Posted by DennyW

That sounds pretty good.
((Sound reasonable to you guys?))
The first thing you need to do when thinking these things out, is think like a thief. How would, and what would you bring, or do to steal your car ?
So far, your on the right track. The more delays you can figure into the system, the better. Time is the thiefs enemy most of the time. Of course, if they have a wrecker, trailer, or some means of just taking the whole thing, your up a creek...unless you put lojak on it...

Funny how they outlaw putting a T vibrator coil on for thief deterrent...They just dance a little...

hey i a have some T coils have to see if they still work i know the one was wired to the back door at one time have to dig them out and make some jacbos ladders up for halloween

Originally Posted by DennyW

Funny how they outlaw putting a T vibrator coil on for thief deterrent...They just dance a little...

What is a T vibrator coil? Is that similar to the old trick of charging a condensor up, to suprise somebody picking up a tool off the metal work bench?