3 replies to this topic

[manthony121]

I'm having a discussion about wiring the Master Switch in a Miata.  The NASA CCR specifies that "The switch should shut off the motor and cut all power except to the on-board fire system, radio communication,and any other life support / medical device."  The SCCA GCR does not have the requirement that the master switch shut off the motor: "The master switch shall be installed directly in either battery cable and shall cut all electrical circuits but not an on-board fire system."

 

It seems to me that the master switch *should* turn off the engine.  Is this an oversight in the GCR?

[chris haldeman]

The switch must stop the engine. Remember all electrical circuits includes but is not limited to ignition,alternator,coil packs ,relays ect.

[manthony121]

I've noticed that the very popular "Dave Wheeler Single Pole Kill Switch" method does not meet the requirements for either the SCCA or NASA.  It wires the positive terminal of the battery directly to the "B" terminal of the alternator, bypassing the kill switch.

[Dave D.]

It wires the "B" terminal t the "+" side of the battery so that when you kill everything and the engine is spinning down, the magnetic field in the alternator collapses which causes a voltage spike, that is easily and conveniently absorbed by the battery. I usually will connect that wire with a fusible link at the end,so if things get really bad, the link will cut the feed( it would have to get really bad to crush the front end so  that the alt wire could be shorted). Dave's diagram is (arguably) the most simple and effective way of wiring up a kill switch in a Miata.