.........cut off switch...........

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70aarcuda said:
I got the two post cut off switch...the alternator return wire goes to the battery side of the switch....flip the switch the engine shuts off..
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Yes but battery power still goes all the way to the front and terminates at the Alt., right?
To eliminate that;wire a relay at the cut-off sw, triggered from the cold side, to complete the circuit between the battery and the alt. Voila;when the cut-off is triggered, the relay dies, and everything forward of the cut-off goes dead. The downside is that anytime the cut-out is passing power the relay is hot, and so is the alt, so don't leave the power on,between weekends.
 
This thread makes my head hurt.

With a single pole, two post cut off. why not just wire the MSD box to the hot side of the cut off? (starter lug) Hot=Red=Dead when the cut off is in the Off position?

Would this not shut down the ignition and cut the engine?
 
When you have a car burn to the ground because the cut off was wired to the minimum standard, you may understand.

There is the minimum standard and there are much safer methods to wire a cut off switch and kill the alternator line as well.

Pick a method and go, all have +'s and -'s from a safety, cost and ease of wiring perspective.
 
Cope said:
This thread makes my head hurt.

With a single pole, two post cut off. why not just wire the MSD box to the hot side of the cut off? (starter lug) Hot=Red=Dead when the cut off is in the Off position?

Would this not shut down the ignition and cut the engine?
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No, and I agree with crackedback. Regardless of actual wording in NHRA rules, or what you "can get away with" because they didn't actually check, you are supposed to "kill all electrical function"

The problem with a two post switch is the same thing as the old wives tale about "testing the charging system." Allegedly, you can remove the battery cable of a running car, and if it keeps on running, "the charging system is OK."

Now the above is NOT true, is NOT a valid test, and may harm the system, but the truth is, a working, charging alternator WILL keep the system alive when the battery is disconnected. Frankly, 4 post (two pole) disconnects are CHEAP CHEAP CHEAP compared to the rest of inflation over the years. I see no reason NOT to wire the thing up and have it WORK.
 
so im a bit lost..

with the key on and msd, just where is the alt power going? it must be back feeding through the large 1 gauge to the battery correct? (through the starter hot lug) so we want a open solenoid on that line when the cut off is off. correct? ( open solenoid in alt out?)

what powers that solenoid to stay hot-open when the shut off is off?
 
What are you referring to?

Back to what I just posted above.........you can have a normal running engine in a car. Remove either battery connector. IF the alternator is charging, the engine will keep right on running.........the alternator is generating power, and feeding it to the rest of the system. So long as the engine speed does not get so slow as to drop off the alternator output, it will run.
 
is the solenoid in the alt charging lead a powered open solenoid? Where dose the 12v to open-disconnect the alt charge wire come from?

is that why you want a four pole single throw cut off? that way you can power the alt off solenoid with the cut off off?
 
Cope
With the factory wiring;If the operator is incapacitated and cannot turn the ignition sw off, the car will continue to run, even tho the safety crew has disconnected the battery.
In order for the car to be shut off, by the cut-off sw, some rewiring is needed. The Alt output has to be separated from the ignition sw or the field circuit has to be broken. With the battery in the trunk, this is easiest done with a 2-pole(4-post) cut-off sw.One side (2posts) disconnects the battery, and the other pole (2 posts) disconnects the alt, which you have previously disconnected from the ignition sw and brought all the way to the battery in the back.The ignition would have to get it's feed from somewhere else, like the the big cable at the start relay.
The difficulty arrises when a fellow tries to do this with just a single pole(2 post) cut-off switch. That's when a relay is substituted for the 2nd pole, and it is triggered from the cold side of the cut-off sw.such that when the cut-off sw disconnects the system, it also de-energizes the relay, which breaks the charge circuit at the battery, and the engine quits, as does everything else electrical..In this way the only hot wire on the car is the short cable from the battery to the cut-off sw, and the short jumper from the hot side of the cut-off sw to the relay. From that point forward, the electrical is dead.
 
Most of the 4 pole switches are not capable of handling alternator charge loads. Most of the small post are only rated to 20 amps.
 
Cope said:
is the solenoid in the alt charging lead a powered open solenoid? Where dose the 12v to open-disconnect the alt charge wire come from?

is that why you want a four pole single throw cut off? that way you can power the alt off solenoid with the cut off off?
Click to expand...

There's a whole BUNCH of ways you could wire this, depending on your car.

You DON'T use the two small switch terminals to kill the "big" alternator charge wire.

You use it to kill something that will kill the "loop."

You can use it to kill ignition, to kill the regulator field circuit, if you are using EFI you can kill the pump relay. What you need is something some circuit which will separate the charging alternator (or kill it from charging) from the ignition and fuel pump.

If you are using MSD, you can use the two extra disconnect terminals to kill the MSD "small red" trigger wire. Run two no 14's from the switch to the front, put them in series from the ignition switch to the MSD "small red." There's very little current there
 
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