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> Master Cut-off switch questions., is it this simple?
GlennCMC70
post Nov 29 2004, 03:37 AM
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i need to start the wiring part of my CMC car build. the only factory wiring thats gonna be used is the engine harness.
i guess when wiring a car, the first place to start is the battery and go from there. when wiring in a master cut-off switch, is it as simple a putting it inline w/ the positive battery lead? i think the alternator feed needs to be on the battery side of the disconect switch, right? i also plan to put the PCM BAT lead there also.
one thing i keep seeing reference to is something to protect the alternator when this switch is flipped. what needs to be done here?
tell me what you know on this please.
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trackbird
post Nov 29 2004, 04:02 AM
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M.A.D. Enterprises had a kit we just used on a Mustang. It put a ford style solenoid in the rear and switched the large hot cable on for starting only. Then, it used a 10 gauge (or 8?) to run the alt to the battery and the power forward (through the cutoff). That way, when you kill power, you kill it to the motor. However, the alt stays loaded by the battery. It was a slick setup.
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GlennCMC70
post Nov 29 2004, 04:31 AM
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i'll be putting in a fod solinoid later. right now i'm more concerened w/ killing parts (as in broken) when the switch is flipped. something to do w/ a voltage spike?
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trackbird
post Nov 29 2004, 04:39 AM
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QUOTE (Glenn98ZM6 @ Nov 28 2004, 11:31 PM)
i'll be putting in a fod solinoid later. right now i'm more concerened w/ killing parts (as in broken) when the switch is flipped. something to do w/ a voltage spike?

I don't think disconnecting a battery from a running alt. is the best thing in the world. The old ones could go as high as 70 volts (old, old, stuff). I don't know how fast the regulator would catch this one. It may not be "good" for the computer and all. I'm thinking that the ford solenoid is the right way and the only safe way to set it up (there may be others, it's getting late and I drove all night last night). I don't think you can do a quickie job to fix later on this one. I may be wrong.
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GlennCMC70
post Nov 29 2004, 04:55 AM
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i'm not looking for a quicky fix. hell the car doesnt even have 1 single wire in it! (IMG:http://www.frrax.com/rrforum/style_emoticons/default/blink.gif)
as for disconnecting the battery from a running alt, thats not what would happen if the 12v output from the alt was put on the battery side of the cut-off switch. if it wasnt, the car would still run. the alt will provide enough output to keep a car running.
the computer (PCM BAT) will also be on the battery side of the switch, thus having 12v at all times. the PCM IGN feed will however loose 12v when the switch is tripped thus killing the 12v to the opti and coil.

i'm mainly looking for feed back on some type of requirement to have a diode in the circuit somewhere to dump the spike. make sence?

here is a link to the reference. looks like a resistor is needed.
http://www.pegasusautoracing.com/productde....asp?RecID=1464
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trackbird
post Nov 29 2004, 05:21 AM
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I'm with you, I thought you were basically looking to put the switch between the battery and everything else and was not thinking about the actual layout. (As I said, I drove all night to get home and I'm fried.....). I'll think about this more tomorrow.

Night!
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rmackintosh
post Nov 29 2004, 04:44 PM
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I bought a 4 pole kill switch. It has 2 big leads for the battery. And two smaller leads for the alternator "power wire" (the little red wire that turns the alternator on).

I run the cable from the battery in the trunk, to the kill switch, to the engine compartment where it is rewired, but essentially stock. I run a small wire from my ignition toggle switch to the kill switch small pole, then to the engine compartment and the small red wire at the alternator. This kills everything

It works fine....been tested many a time.

The rest of your plan sounds fine....I wouldn't worry about resistors and such...won't be necessary....but if you want....go ahead.

One mistake I did do was put the PCM on the "killed" side of the system....oops....lose my learned parameters EVERY TIME (IMG:http://www.frrax.com/rrforum/style_emoticons/default/banghead.gif) I will fix that this winter.... (IMG:http://www.frrax.com/rrforum/style_emoticons/default/thumbup.gif)
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brannanjohn
post Dec 2 2004, 01:37 PM
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This is my next project. Where did you get the kill switch. Is it one from peagusus? or another brand?

Please let me knwo how it works out.
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rmackintosh
post Dec 2 2004, 04:37 PM
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I got the Longacre one that comes with the aluminum mounting plate....there is no removable key with that unit
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CMC#5
post Dec 8 2004, 08:43 PM
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You guys running in sanctioned events might want to read the requirements of your particular sanctioning body for kill switches. Nasa, for example, requires the kill switch to shut off power to everything that is not the fire system or other life support/medical device. aka nothing is on the battery side of the switch except the battery.

I used one of the longacre four pole switches and cut the excitation current to the alternator (as Randy) with the secondary pole to eliminate the voltage spike and the motor. I never use the kill switch. I have a regular old ignition key to turn it on and off! (IMG:http://www.frrax.com/rrforum/style_emoticons/default/laugh.gif)
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rmackintosh
post Dec 8 2004, 10:04 PM
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QUOTE (CMC#5 @ Dec 8 2004, 02:43 PM)
...the excitation current....

oh Al......don't talk like that....its SO sexy!

(IMG:http://www.frrax.com/rrforum/style_emoticons/default/rotf.gif)
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Jon A
post Mar 28 2005, 12:16 AM
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QUOTE (CMC#5 @ Dec 8 2004, 12:43 PM)
Nasa, for example, requires the kill switch to shut off power to everything that is not the fire system or other life support/medical device. aka nothing is on the battery side of the switch except the battery.

Well, damn, SCCA is the same. Where can I find more info about that Ford Solenoid? I'm not even sure that would technically be legal....

The whole reason I haven't relocated my battery yet is I didn't want to have to run 30 ft of welding cable all over the car. I guess I might need to anyway....

Yes, I need the switch just for timed laps in Solo I. Err, no, I wouldn't have in our region's Solo I last year, but now that the 400lb Gorrilla is in charge of the Time Trial rules, I do...among other things.... (IMG:http://www.frrax.com/rrforum/style_emoticons/default/banghead.gif)
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Zimm
post Apr 5 2005, 05:21 PM
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QUOTE (rmackintosh @ Nov 29 2004, 10:44 AM)
I bought a 4 pole kill switch.  It has 2 big leads for the battery.  And two smaller leads for the alternator "power wire" (the little red wire that turns the alternator on). 

This is on my to-do list as well. Just wondering what gauge wire are you guys are running for the alternator leads?
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CMC#5
post Apr 6 2005, 07:22 PM
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I don't remember the size exactly, but I used the same as the OEM wire running to the alternator originally
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