Master disconnect switch

[blown69nova]

I am wiring my NHRA legal battery disconnect and I need to know what terminal on the back of the alternator I need to connect to the master switch. Is it the large battery terminal or the small jumper wire?

Thanks, Steve

[vintageracer]

I do not believe you want anything other than the 2 positive cables attached to the master ON/OFF switch. On my race cars the master switch is inline on the positive cable between the battery and the starter solenoid. I run a 1 wire alternator and that wire ultimately goes to the solenoid.

Remember, the master switch must allow the car to shut off (stop running) when turned to the off position on the switch. Go to www.madelectrical.com for lot's of automobile wiring information and pre-fabricated harness's.

[blown69nova]

I know about the positive cable, but I believe they want a car that has a charging system to cut that circuit also because the alternator can backfeed current back to the ignition system. The switch I have is from Cole Hersey and has 4 terminals- two for the pos. batt. cable and two for the charging system.
I'm just not sure which terminal on the alt. to use. The large stud is the charging wire to the batt., the jumper wire from the internal regulator to the large stud senses batt. voltage and the other terminal goes to the dash light. The question is which one makes sense to cut?
Any other thoughts on this are appreciated.
Thanks, Steve

[HzEmall]

If you kill the alternator and stuff with a kill switch during "tech" you can fry the alternator and or ignition box.

[vintageracer]

Never had that happen!

However I DO NOT have master kill switches designed as described by the original poster with 4 lugs to allow the alternator to be wired to the master kill switch.

I have the old tried and true 2 lug kill switches that kill that main power.

[Overkill]

I know about the positive cable, but I believe they want a car that has a charging system to cut that circuit also because the alternator can backfeed current back to the ignition system. The switch I have is from Cole Hersey and has 4 terminals- two for the pos. batt. cable and two for the charging system.
I'm just not sure which terminal on the alt. to use. The large stud is the charging wire to the batt., the jumper wire from the internal regulator to the large stud senses batt. voltage and the other terminal goes to the dash light. The question is which one makes sense to cut?
Any other thoughts on this are appreciated.
Thanks, Steve

Run the alternator wire back to the same side of the switch that your battery is connected to or to the battery itself. That way when you turn the switch off, there isn't anyway that it can back feed and keep the car running. I used an 8 gauge wire on mine to make sure that it was a large enough wire to keep the system charged.

[blown69nova]

Not to disregard Anyone's reply (which I appreciate!), but here is what the electrician I work with says: The only reason the alternator is kept from feeding back to the ignition switch, is the diode in the wire between the #1 term on the alt. and the dash light which then goes to the ign. switch. This is why the master switch will cut power to the ignition and kill the engine. Remember when we all went to the internal regulated alternators and had to add the diode so the ignition switch would kill the car?
My point is; if something happened during a crash, or that diode simply failed, the vehicle could theoretically still run after the master cutoff was turned off because the alternator is now still feeding power to the ignition.
Thanks for the replies,
Steve

[Fuelie Fan]

I don't know what the NHRA rules are, but I think that the simplest solution would be to put the disconnect on the ground side...

[alky]

Blown69, 2 terminals for the battery to starter disconnect and 2 terminals for the alternator main power wire that normally goes to the starter.

[blown69nova]

Thanks for the replies guys!