Do I want to relocate my battery?

[2fnloud]

Yeah but NHRA states that you must switch the positive side of the battery.

[J. Fast]

Most sanctioning body race rules require a positive disconnect. The disconnect must isolate the battery/ alternator from the fuse block and starter.

I have helped build and wire 10 different styles of racecars and all are positive cutoff.





Red wire across dash bar is positive kill to main fuse panel.

[Intropy]

So are the people who do this running wires back from the alternator?

[2fnloud]

No I don't think so. I think they are using a high amp relay. You would mount the relay in the engine bay and it has four terminals (2 big, 2 small). The two big ones are for the 4/8 gauge that is the main cable from the alternator. The two small ones: One is a ground, the other small one would run like 22GA wire back to your master switch that typically is at the bumper of the car.

You would also have the battery wire (0/1GA) wired into the master switch as well. When the master switch is on it will allow the battery to connect to the front and charge the 22GA wire to the relay under the hood to allow the alternator to connect to the car's electrical as well.

Turn the switch off, the battery is disconnected as well as the wire to the relay and that will cause the relay to trip and disconnect the alternator as well.

But this will also erase anything that needs the battery (12V) to keep memory...say clock, radio settings, AEM settings (just guessing here IDK if a tune is flashed to a memory, or if it needs a 12V constant to keep the tune in the memory.

Perhaps it would be best to wire a relay into the ignition circuit so when the switch is turn off the ECU / EMS would think that the ignition fuse blew....

Any input anyone?

[2fnloud]

They say a picture is worth a thousand words:


This first diagram will cut the battery AND alternator from the car's electrical system, This should be NHRA legal.
The second diagram will keep the battery AND alternator connected to the car's electrical system and the switch will now disconnect the ignition & fuel pump circuits. This will not be NHRA legal but it WILL cut the fuel and ignition off and allow you to keep the constant 12V needed for radios clocks and whatever.

This second one should satisfy every tech assuming you are a street driven car and not a pro-street or top fuel dragster.

I do not like the idea of suddenly separating the voltage from a running vehicle, I was told that it can do bad things to the ECU.

[J. Fast]

Using this style of disconnect...




I drafted this wiring diagram for future reference.



The ARC protection is the resistor. This is a very safe and smart way to disconnect power.

[2fnloud]

J, that will have no ill effect on the ECU? Or is that what the resistor is for?

And what wire would we use when there is coil packs?

[J. Fast]

J, that will have no ill effect on the ECU? Or is that what the resistor is for?

And what wire would we use when there is coil packs?

Nope, no ill effect on ecu. The resistor is for possible surge off the alternator.

Kill the power to ignition at the PTU. PTU feeds all 3 coil packs.

[2fnloud]

The only thing I see now is that you would still wipe out your constant 12V to devices that need it...is that correct?

[J. Fast]

The only thing I see now is that you would still wipe out your constant 12V to devices that need it...is that correct?

That's correct. All power is cut. However, the only device that will get wiped is the clock.