I searched but cant find the number of the two pole cut off switch that most are using.

http://www.littelfuse.com/indu...onnect-switches.aspx

I use the 2484A...

When selecting a master cut off, remember that a higher amp rating is best. The switch needs to be rated for the starter draw amperage which can exceed 200 amps. [ a switch rated for 200 amps will briefly exceed that rating so consider 200 amp rating the minimum.]

Larry is correct as fas as looking for amp rating but all switches have a continuous rating and an intermittent rating (for cranking) see spect below on a C/H switch. This is all someone would need.

Rating: 6-36 Vdc; Large studs 125A continuous - 1000A intermittent 15 sec. On 5 min. Off;

The 75912BX is the one you want with 4 3/8" terminals so you can turn off the alternator as well. The Moroso 74108 is that Cole Hersee switch rebranded.

This message has been edited. Last edited by: 183N,

diceman1540 As 183N replied the 75912BX switch is the one you want, even if you don't use the other 2 posts now...183N also turned me on to Amazon Prime for that switch & saved over $20

I asked Powermaster,Eastcoast and Mechman, all said killing the power to the alternator with the engine running will hurt the alternator. Since that's one of the test methods of some techs killing the alt power can be bad.

quote:

Originally posted by Eman:
I asked Powermaster,Eastcoast and Mechman, all said killing the power to the alternator with the engine running will hurt the alternator. Since that's one of the test methods of some techs killing the alt power can be bad.

That may be true, but are you routinely using your master switch to shut down the car with the engine running??? I turn my switch on in the morning and off at the end of the day. If some track official needs to shut me off in an emergency when I'm upside down in the weeds, I'm not real worried about my alternator!

I never leave the power on in the race car...it is turned on when I am moving it, cooling it, or racing it, and turned off otherwise.

Cant kill a battery of you don't leave the power on and clearly conserve the battery by turning power off when not using...JMO

Works for me...others have there own routines that work well for them.

There are other ways to kill an engine with the main disconnect switch in the back without touching a single wire to the alternator.

Anyway, you shouldn't be using that switch to shut off a running engine anyway, that is why we have ignitions switches of some sort.

My disconnect gets used twice a day, once in the morning after I roll the car out of the trailer, and once again after it is loaded back in the trailer, hopefully with a few extra $$ in my pocket.

quote:

Originally posted by Eman:
I asked Powermaster,Eastcoast and Mechman, all said killing the power to the alternator with the engine running will hurt the alternator. Since that's one of the test methods of some techs killing the alt power can be bad.

The only time the switch would actually kill the alternator power with the engine running would be in an emergency, otherwise you’d use the ignition switch.

The rule book requires that the power switch stops the engine from running. Unless you have a 4 post switch like the one mentioned, in a 1 wire alternator setup usually the alternator wire goes directly to the battery. While this will shut the car off, the wire from the battery to the alternator will always be hot. I don’t like that. The other way to wire it is with the alternator going to the car side of the master disconnect. In this case the alternator wire won’t be hot with the switch off but the switch also won’t shut the engine off since the alternator is connected to the ignition and will power it as long as the alternator is charging.

I have to clarify, I never use the master cut off to turn car off. My cars will turn off with master cut off and do have alternators. I do turn the power off after I turn water pump and fan off too cool, and avoid charging car with power on otherwise.

Just habits we all develop thru years of racing...may or may not make a difference.

75904-1

quote:

Originally posted by 1leg:
75904-1

This switch has the small 10-32 terminals for the alternator, only rated for 20a continuous.

quote:

75904-1

We have never had a issue on our race cars.

quote:

Originally posted by 183N:

quote:

Originally posted by 1leg:
75904-1

This switch has the small 10-32 terminals for the alternator, only rated for 20a continuous.

That is plenty. Can kill the fuel pump relay on an EFI setup, or kill the ignition on a carb setup. Alternator never has to go back there, ever.

quote:

Originally posted by BD104X:

quote:

Originally posted by Eman:
I asked Powermaster,Eastcoast and Mechman, all said killing the power to the alternator with the engine running will hurt the alternator. Since that's one of the test methods of some techs killing the alt power can be bad.

That may be true, but are you routinely using your master switch to shut down the car with the engine running??? I turn my switch on in the morning and off at the end of the day. If some track official needs to shut me off in an emergency when I'm upside down in the weeds, I'm not real worried about my alternator!

Just to clarify, no I don't shut my car off with the master cutoff. Just a heads up that if it is done, like when a tech guy does it, you might have a damaged alternator.

Instead of running a heavy alternator cable all of the way back to the switch or battery just run it to the junction for the battery cable to the starter. many cars have a pass through or use a Ford style solenoid. You can cut the wire size down considerably if you're only running it a few feet to the firewall or floorboard. Then you can power everything else with the other set of terminals on the master disconnect so the alt. can't feed into it and keep the car running.

not to highjack thread, but anyone know about this new electrical master cutoff deal ive seen installed in cars instead of cables?

quote:

Originally posted by DRB Motorsports:
not to highjack thread, but anyone know about this new electrical master cutoff deal ive seen installed in cars instead of cables?

I've looked at a couple, they sure are proud of them as far as cost goes...until my cable setup fails, I'll stick with what I have....

The only issue I have ever seen from using a kill switch during a tech inspection came from a stupid NHRA tech guy who flipped the switch off and then back on again very quickly.

It did not kill the alternator but it did kill the MSD box.

Make sure and communicate to them before they do the test that you need time to turn off everything in the car before they turn the switch back on.

The constant duty solenoids work very well. Wire two switches in series for the solenoid coil, one at the back of the car and one inside the care. That way either switch will kill the voltage to the coil and disconnect the battery.

First car I wired with one was a 71 Maverick back in 1978.