NHRA legal kill switch - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 2 Old 04-17-2016, 09:44 PM Thread Starter
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NHRA legal kill switch

Just looking for an nhra legal kill switch wiring diagram for a fox. Rear mounted battery and disconnect switch, stock alternator.

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post #2 of 2 Old 04-17-2016, 10:29 PM
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Originally Posted by boostup89 View Post
Just looking for an nhra legal kill switch wiring diagram for a fox. Rear mounted battery and disconnect switch, stock alternator.
I spent a long time thinking about a safe way that would make the NHRA happy and not be a grave risk to my car or me.

I eventually decided to use a double switch like this:

Moroso Super Duty Battery Disconnect Switches 74102 - Free Shipping on Orders Over $99 at Summit Racing

One side kills all the electrical feeds to everything low current that makes the car run by opening the Ford ignition key power lead. There is only about 35 amps in my car maximum on the key run feed, so I just used a fused number 8 AWG up to the ignition key supply.

Killing the feed to my ignition key (and low current stuff) stops the fuel pump relay voltage, kills the 12V run wire to the Holley EEC, kills the alternator field supply feed, and kills everything low current fed from the ignition key. That way the alternator spike from disconnecting the battery cannot hurt my radio, ignition box, fan controllers (it opens the fan and water pump feed relays), or Holley.

The other large high amperage section opens the big battery cable to the starter, which branches from the starter to all the high current feeds and the alternator output.

I still don't completely like this, but at least it satisfies the NHRA and it is not the worse thing for car and driver safety.

Unfortunately what works in my car with my wiring might not work for anyone else.

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89 LX. 363, single turbo, Super Vic EFI, TFS high port heads by TEA, solid roller, glide. Holley HP EFI. (exact combo varies)
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