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Discussion Starter · #1 · (Edited)
well think i know but lets see

going to fit a battery kill switch now if im going to do it propperly would i have both power cables from the alt going to the battery as if i leave it as one cable to battery(switch at positive) it would still run on thru the alt correct or no

and i got just the battery kill not fia master battery kill thanks
 

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A battery master switch isn't the same as engine kill switch. You do need an FIA type battery master/circuit breaker that wires the ign through the switch and has a resistor to dump the load to prevent the alternator diodes frying.

I don't think you can run the alternator live through the battery switch - well maybe that one time before you fry the diode pack.
 

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Made that mistake with mine. Hit the battery kill switch with the engine still running; cost me an alternator!!
 

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Discussion Starter · #6 · (Edited)
please run this by me as i think differnetly if the cut off is just before the battery and the alt goes direct to the battery then the last charge would go in the battery... would it not ?? therefore killing nothing or am i just misunderstanding something
 

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There are two ways of looking at this. One is the race way where cutting off the engine in an emergency is the prime importance. (Marcs method and required in certain race authorities). The second is done to cut power to everything:
Referring here to one wire alternators and two post kill switches.

In the first you wire the power lead of the alternator to the battery side of the switch. In an emergency when say a marshall flicks the switch on a still running crashed car the engine will cut out. This is because the alternator is now taken out of circuit with the ignition system and so it can't backfeed and keep the engine running. The priority with a race car is to switch off the engine. The downside is that when the car is parked and the kill switch in the off position then that power lead/alternator internal is still live.

In the second you wire to the output side of the kill switch. In that same crash scenario when the switch is turned off the alternator output can backfeed the ignition and the car will keep running. Not desireable in racing. The plus side is that when parked and the switch is in the off position then everything is dead and isolated from the battery.

As said above you can get an FIA type switch which has extra terminals to wire a three wire alternator and prevent killing the alternator if you choose to. Also as Marc says fuse the alternator power lead and I use a really heavy gauge wire based on the alternator output value.
 
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