FrontEngineDragsters.Org Forum

Technical => Spud Miller's Cave => Topic started by: noslin on December 31, 2018, 03:20:00 PM

Title: grounding mag
Post by: noslin on December 31, 2018, 03:20:00 PM
concerning the mag kill switch.  diagrams show from ground to switch to ground @ coil.   question is for the ground to chassis or ground to motor or ?   i have small 12v battery for dash and electronics.  the ground is floating and not directly to chassis anywhere.

so, where does the 'chassis' ground get connected too on the kill switch?  to the motor, mag base, battery and then ground battery to chassis, or ??? 

thank you
Title: Re: grounding mag
Post by: jeff/21 on January 01, 2019, 01:56:40 PM
i grounded it to the motor using steel core plug wires
Title: Re: grounding mag
Post by: dreracecar on January 02, 2019, 09:36:00 AM
To the stud holding the trans to the engine thru the motorplate,  everybody happy
Title: Re: grounding mag
Post by: Spud Miller on January 03, 2019, 10:00:33 AM

 Ultimately, the mag is defeated when the positive coil terminal is shorted with the negative coil terminal. The best mag ground is the other side of the coil.

 Instead of running a single wire from the (+) coil terminal to the kill switch and then grounding the other side of the kill switch to the chassis or another local component, run 2 wires from the (+) and one (-). Attach one to each kill switch terminal. That's as good as it gets.

Title: Re: grounding mag
Post by: THE FRENCHTOWN FLYER on January 03, 2019, 04:24:24 PM
Be aware that NHRA rules dictate that the engine must shut off when the external vehicle shut-off switch is turned off by track personnel. I got bounced by an NHRA tech official when the outside switch did not kill the mag. To be NHRA legal you must run the ground kill through a relay that is powered up by the electrical system and is powered down when the external shut-off switch is activated.

Also, I use the mag kill switch when starting because I use a locked mag with lots of cranking advance.
Title: Re: grounding mag
Post by: Spud Miller on January 03, 2019, 05:06:34 PM

 Yes, good point on the master disconnect mag kill...

 For points mags I recommend one of these to ground the ignition when the master switch is thrown: (

 For Pro mags, one of these works terrific: (


Title: Re: grounding mag
Post by: dreracecar on January 03, 2019, 06:03:40 PM
external kill switch (besides the one for the driver) is only required if the car is self starting (along with nutral safety switch) cars using a remote Blower starter, its not mandated to have a switch at the back of the car
Title: Re: grounding mag
Post by: noslin on January 03, 2019, 10:16:36 PM
its a hunt or vertex mag with external coil.   images ive seen on net show to ground >> switch >> coil ground.   so to confirm, one side to positive and other side to negative on the coil for kill switch.   ( power >>> switch >>> ground) just seem like it would mess up something putting power to ground on the coil.   but, thats how the RPM Rev-Limit Relay is wired so must be ok haha.

its interesting there is a distinction between blower starter or remote battery start versus on-board start for external kill switch.  would seem once the motor is running regardless of how started they would want a kill switch.   i guess the idea is down track if an accident happens they can kill power to prevent from restarting once on-seen?  just seems odd why nhra wants one for on=board starter/battery setups and not for remote starter/battery setups.  i did not wire in an external switch.

Title: Re: grounding mag
Post by: dreracecar on January 04, 2019, 08:39:23 AM
If they made rules for every combination the book would be a foot thick and small type.  So they lump that every car that carries an on-board battery for starting is required to have an external kill switch along with a neutral safety switch to prevent accidental starting of the car.  The switch at back of the car pertains to cars with an electric fuel pump that keeps running after the crash feeding the fire until the power is shut-off.  Blown cars on the other hand are brought to the line in neutral  be it a PG or Lenco/High gear and has to be started by getting second person envolved. Generally speaking , a blown car is shut off with the fuel pump and not ignition
Title: Re: grounding mag
Post by: coupemerc on January 04, 2019, 11:51:50 AM
I agree with Bruce above on the remote kill switch. I got bounced by a local tech guy because my J/F car did not have a remote kill. I told him that it is only required if the car has a battery. Generally, J/F cars with a mag do not carry a battery. He still bounced me. I had to take my case to the NHRA D1 office and then to Glendora. They ended up agreeing with me. You may WANT to put an external mag kill on a car with no battery but it is not REQUIRED.
Title: Re: grounding mag
Post by: noslin on January 04, 2019, 05:24:06 PM
thank you for the replys everyone.  the tracks we would run at i dont think we'll have an issue but i do understand.  if it happens down the road then ill pop one out back.
Title: Re: grounding mag
Post by: George on January 05, 2019, 05:23:30 AM
I have used the Flaming River combo master kill . Part No.: FR1010 . It was cable operated from the rear of the car. Also had a mag switch in the drivers area.