Battery disconnect for rear mounted battery

This is what my local tracks website says about relocating the battery to the trunk.


Won't the car still run if you hook up the push/pull switch to the positive side of the battery? How do make this work and be legal for track duty?

Master Disconnect Switch: Whenever a battery is relocated to the trunk, the vehicle must be equipped with an external disconnect switch. This switch must be clearly labeled and immediately disconnect the positive side of the battery. To determine if the switch operates properly a tech inspector will turn off the switch with the engine running. If this action does not shut down the engine then the switch is wired improperly and the vehicle shall fail the inspection. Drivers should ensure the alternator charge wire is routed to the battery side of the switch. This isolates the alternator from the rest of the electrical system. Drivers should check with the switch manufacturer to ensure it is properly installed.

I don't think the car could run if you make a break in the car's electrical circuit, if you cut the battery and the alternator on the same circuit the motor will have no electricity to spark, run sensors, injectors, etc.

You muct run the alternator wire to the disconnect switch at the back of the car and hook it to the battery side. When you push or turn the switch it will dissconnect the battery and the alternator from teh entire electrical system and kill the motor.

Just disconnecting the battery won't kill the engine. The alternator will feed back into the system and provide voltage to the ignition. You can also try wiring in a relay that feeds the alternator field wire. If the main power is disconnected, the relay will disconnect the field wire and since the alternator won't charge, the ignition has no power. Another way is to use a relay to feed the ignition power. Same thing, disconnect the battery and the relay disconnects the ignition.

Other things to consider when installing a master shut off switch.

Must not be made of plastic
Must not be keyed.
Off needs to be clearly marked
If installed as a push/pull, push is the off position.

Using a master switch in a race car isn't a big deal. Using one in a modern street car can be a pain. Radio presets, clock, etc all get wiped out.

I'm still not sure if my way is legal or not, but, I routed the fuel pump and msd power wire to the switched side of my switch. When the switch is turned off, the car shuts off (no fuel or ignition). The battery and alternator and everything are connected to the other side, so, the rest of the car does not lose power, just the fuel pump and ignition.

This way, you don't lose radio presets, clock, etc..

--Sean

Probably have to be a judgement call by tech. I'm sure if it kills the engine, they'll be happy. With modern cars and EFI, I'm sure the electric fuel pump kill is also a good idea. No fuel, no ignition, engine dies. Having a radio or electric fans still on isn't going to be a big problem when you're on your roof and the safety crew have shut off the master switch. I guess the biggest fear would be still having something like electric fans running, you're on your roof and there's a fuel spill.

The rulebook states "must stop all electrical functions"

That covers everything just to keep everyone safe.