kos11-12

Hi everyone,
I am trying to resolve an electrical issue with my car, I am renewing my cutoff 6 connection switch, and have a question:
Mine originally did not have the jumper wire plugged on W (2) and the resistor wired to the body, does anyone knows how critical that could be.
Thank you
hank you

robt964

The kill switch isolates the battery from the entire electrical system of the car. If this is operated whilst the engine is running, the alternator will loose its 12v reference voltage and cause it to drive the voltage UP. The very low ohm resistor and jump wire are there to prevent this from occurring. Operating the kill switch completes the circuit so that the vehicle supply side is tied to ground, and any residual current produced by the alternator is dumped through the resistor. Both this and the circuit that breaks the coil supply are important in stopping the motor safely without risk of electrical damage or run-on.

kos11-12

HiWind

aha that's a great insight thanks RobT ... so cut-offs wired on the battery negative/ground are just for use when the car is not running ie to save the battery?

pelican thread

robt964

When placed on the -ve side, that is correct. Again tho, in that configuration the kill switch should never be operated whilst the engine is running - it will likely cause damage to parts of the electrical system through over voltage.

Gus

Is it necessary to wire up the “Z” terminals from ignition switch and to coils. Won’t kill switch still function without these terminals connected?

robt964

It depends on the specifics of the application / construction of the electrical systems. In general though, with a running engine the battery is completely redundant outside of providing an excite voltage and output reference to the alternator. The car/engine's electrical system is powered entirely from the alternator.
Disconnecting the battery will therefore on its own not be sufficient to stop the engine. The battery is no longer the power source. What typically happens is that the engine will run-on. The voltage produced by the alternator will quickly continue to rise until some vital electrical system of the engine is damaged and causes the engine to stop. Both the resistor n/o circuit and the coil n/c circuit work together to ensure a safe shutdown. Neither of those two circuits on there own could guarantee a safe shutdown.
I would rather have no kill switch than one that wasn't wired in correctly. If somebody pulls it, its either not going to work as hoped and at worse let the smoke out of something expensive.