Kill/Cutoff switch wiring help

[msteele]

I know this subject has been beat to death but I can not figure out how to wire the kill switch for racing. Engine has to be killed at 3000 rpm without frying the alternator.

The car is a 1980 911 SC.
Cut off switch is a long acre 4 pole switch.
I also have a NC/NO 12v relay and a 10w 3.3 ohm resistor.

For reference lets label the 4 pole switch.
A. big lug on hot side.
B. big lug on switched side.
C. small log on hot side.
D. small lug on switched side.

Relay has 4 connection.
E. 12v to activate the relay.
F. 12v in on hot side to be switched.
G. NO
H. NC

I have figured out the following so far.
Connection A. goes to the battery.
Connection B. goes to the rest of the car including alternator.
Connection C. goes to the ignition from the fuse panel.
Connection D. goes back to the fuse panel.
Relay connection G or H goes to the resistor witch goes to ground.

Please do not suggest I buy a 6 pole switch. The long acre switch is maid a lot better than the cheap plastic 6 pole switches available.

The problem I currently have is where to hook up the relay. If I hook it up to connection B the alternator will feed back and keep 12v to the relay thus not tripping it. If I hook it up to connection D, when I turn the ignition off, the relay will be tripped shorting the battery to ground, (Not good).

Please help,

Mark

[#391]

I just wired up a kill switch last week. I have the Longacre 4 pole switch sitting on a shelf because I couldn't figure out how to wire it up properly. I ordered the 6 pole switch, which was fairly simple to wire, and properly dumps any potential power spike from the alternator to ground.

Sorry it's not what you wanted to hear. Maybe someone else will chime in with the proper method of wiring a 4 pole switch. I certainly agree that the Longacre 4 pole switch is much more substantial than the alternative 6 pole.

I made this diagram for the 6 pole (you can substitute the coil for the ignition if it's easier for your application) just in case you reluctantly decide to use one:

[Eagledriver]

I think if you hook it up to the alternator it will lose power when the engine stops due to the ignition cut-off from the switch. This will work but it's not a very good set-up because you will need to have the relay supplied with power all the time and it will drain your battery unless you turn off the kill switch all the time. I suppose you could feed the relay with switched 12 volts from the ignition switch. I think the best thing to do will be to draw out your ideas to see what all the possible paths are.

-Andy

[JoeMag]

sorry, but i'd recommend the 6. see below. has wiring diagram. had one on my 930 race car and it worked fine. I think the wiring is very straight fwd. I like that it drains alt to ground through resistor so you're not going to get that inducive kick and opens up what ever ignition wiring you want.

http://www.pegasusautoracing.com/productdetails.asp?RecId=1464

[msteele]

Ok, after looking at all the possibilities I give up.
I bought a 6 pole switch and hopefully it will not have any problems.
Much simpler to wire and I do not have to worry about burning up the alternator.