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Power Cut Off switch Question. #1599655 03/28/14 02:20 PM 03/28/14 02:20 PM
Joined: Feb 2006 Posts: 474 Alberta, Canada 451Guy OP mopar
451Guy OP mopar Joined: Feb 2006 Posts: 474 Alberta, Canada	Last summer I finally got my car back to the track to make some passes. I had done a ton of stuff to it over the winter and one of the upgrades I made was installing an alternator for the first time. When I went through tech the inspector turned off the main power switch and the car kept running. I have since been told that I need to put a diode in the excite wire to solve this. I am getting ready to do this but I have no idea what size of diode I will require. The alternator is a 55 AMP Denso unit. Any input will be appreciated. Thanx 451 Guy 512 cu in 71 Demon Super Street Car - NO LONGER - Broke Crank Best ET 9.57 @ 139.96 451 cu in Pump Gas - 71 Demon Super Street Car Best ET 9.99 @ 136.80 512 cu in 69 Charger R/T Best ET 11.39 @ 118.11

Re: Power Cut Off switch Question. [Re: 451Guy] #1599656 03/28/14 03:18 PM 03/28/14 03:18 PM
Joined: Oct 2004 Posts: 8,165 Left Coast B BobR master
BobR master B Joined: Oct 2004 Posts: 8,165 Left Coast	Quote: Last summer I finally got my car back to the track to make some passes. I had done a ton of stuff to it over the winter and one of the upgrades I made was installing an alternator for the first time. When I went through tech the inspector turned off the main power switch and the car kept running. I have since been told that I need to put a diode in the excite wire to solve this. I am getting ready to do this but I have no idea what size of diode I will require. The alternator is a 55 AMP Denso unit. Any input will be appreciated. I used to run a switch on my alternator that I could control from inside the car.

Re: Power Cut Off switch Question. [Re: 451Guy] #1599657 03/28/14 03:37 PM 03/28/14 03:37 PM
Joined: Aug 2003 Posts: 43,173 Bend,OR USA C Cab_Burge I Win
Cab_Burge I Win C Joined: Aug 2003 Posts: 43,173 Bend,OR USA	Another option is to run the big battery charging wire from the alternator to the battery side of the switch so the alternator will charge the battery when the motor is running but it will not supply voltage to the electrical system when the cut off switch is turned off My car is that way, I used a #10 wire from the alternator ran directly to the battery + post connection Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

Re: Power Cut Off switch Question. [Re: Cab_Burge] #1599658 03/28/14 03:41 PM 03/28/14 03:41 PM
Joined: Jan 2008 Posts: 350 Sidney,Ohio C challenger1320 enthusiast
challenger1320 enthusiast C Joined: Jan 2008 Posts: 350 Sidney,Ohio	Just put the disconnect on the ground cable

Re: Power Cut Off switch Question. [Re: challenger1320] #1599659 03/28/14 03:48 PM 03/28/14 03:48 PM
Joined: Jan 2003 Posts: 13,363 Marion, South Carolina [><] an8sec70cuda I Live Here
an8sec70cuda I Live Here Joined: Jan 2003 Posts: 13,363 Marion, South Carolina [><]	Quote: Just put the disconnect on the ground cable If I'm not mistaken, the NHRA and IHRA rulebooks both state the cutoff has to be on the positive side. CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax

Re: Power Cut Off switch Question. [Re: challenger1320] #1599660 03/28/14 03:50 PM 03/28/14 03:50 PM
Joined: May 2003 Posts: 1,751 Graham, WA P Polarapete top fuel
Polarapete top fuel P Joined: May 2003 Posts: 1,751 Graham, WA	Sorry, NHRA rules require the cutoff switch be in the positive cable, not negative. It would seem to work the same, if the wreck caused no body damage, but if it did and the negative cable was grounded before the switch by being cut the circuit would still be live and the switch would have no effect I wanted to run it through the ground, too. It would have been easier, but you have to consider all possibilities or there is no point to doing it at all. 1986 Dodge Ramcharger 440 2wd, Bracket Racer Under Construction 1998 Ram 2500 QuadCab, new daily driver. 2008 Honda Element 2014 Carry-On 7x14 Cargo Trailer

Re: Power Cut Off switch Question. [Re: 451Guy] #1599661 03/28/14 04:15 PM 03/28/14 04:15 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	The simplest way is to just run the alt output wire to the battery side as Cab said.... there are other ways to do it but thats the easiest and the best way

Re: Power Cut Off switch Question. [Re: Cab_Burge] #1599662 03/28/14 04:16 PM 03/28/14 04:16 PM
Joined: May 2009 Posts: 511 Temperance, MI 6 68 HEMI GTS mopar
68 HEMI GTS mopar 6 Joined: May 2009 Posts: 511 Temperance, MI	Quote: Another option is to run the big battery charging wire from the alternator to the battery side of the switch so the alternator will charge the battery when the motor is running but it will not supply voltage to the electrical system when the cut off switch is turned off My car is that way, I used a #10 wire from the alternator ran directly to the battery + post connection thats how i did my dart, works good. 68 Dart GTS "HEMI" 10.30 @ 131 pump gas street car 3780# 69 Roadrunner 511 six pack 10.92 drive to track street car

Re: Power Cut Off switch Question. [Re: challenger1320] #1599663 03/28/14 04:22 PM 03/28/14 04:22 PM
Joined: Aug 2003 Posts: 43,173 Bend,OR USA C Cab_Burge I Win
Cab_Burge I Win C Joined: Aug 2003 Posts: 43,173 Bend,OR USA	Quote: Just put the disconnect on the ground cable The alternator will continue to supply voltage to the motor through the various engine to body grounds so shutting the switch off will not kill the supply of electrons to the ignition, trust me on that All electron flow from batterys is from the negative post through that cable to the to the motor and returns to the positive post of the battery, not from the positive to the negative like most people think That makes the negative cable not a good idea to hook up to the cut off switch Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

Re: Power Cut Off switch Question. [Re: Cab_Burge] #1599664 03/28/14 04:28 PM 03/28/14 04:28 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	Quote: Quote: Just put the disconnect on the ground cable The alternator will continue to supply voltage to the motor through the various engine to body grounds so shutting the switch off will not kill the supply of electrons to the ignition, trust me on that All electron flow from batterys is from the negative post through that cable to the to the motor and returns to the positive post of the battery, not from the positive to the negative like most people think That makes the negative cable not a good idea to hook up to the cut off switch Wouldnt matter anyways... after you start the car you can take the battery out and it'll run fine.. it has to open the alt output circuit

Re: Power Cut Off switch Question. [Re: MR_P_BODY] #1599665 03/28/14 05:02 PM 03/28/14 05:02 PM
Joined: Jan 2003 Posts: 27,421 Balt. Md 3 383man Too Many Posts
383man Too Many Posts 3 Joined: Jan 2003 Posts: 27,421 Balt. Md	Most I know do what Cab says and run the alt output wire to the battery side of the cutout switch. Another option is like I did years ago on my bracket car and that was I put a toggle switch on one of the field wires and ran it inside the car so I could kill the charging system when I made a pass and you can also just kill the charging circuit when going thru tech with that toggle switch in the car so it dies when the kill (cutout) switch is turned off. It is alot less wire to run if you just tap into a field wire and run it in the car within the drivers reach on a toggle switch. I burned out a rotor on my bracket cars alt so thats one reason I would kill the charging system when making a pass. Ron Last edited by 383man; 03/28/14 05:03 PM.

Re: Power Cut Off switch Question. [Re: 383man] #1599666 03/28/14 05:12 PM 03/28/14 05:12 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	Quote: Most I know do what Cab says and run the alt output wire to the battery side of the cutout switch. Another option is like I did years ago on my bracket car and that was I put a toggle switch on one of the field wires and ran it inside the car so I could kill the charging system when I made a pass and you can also just kill the charging circuit when going thru tech with that toggle switch in the car so it dies when the kill (cutout) switch is turned off. It is alot less wire to run if you just tap into a field wire and run it in the car within the drivers reach on a toggle switch. I burned out a rotor on my bracket cars alt so thats one reason I would kill the charging system when making a pass. Ron Dont let the tech guy see you with a separate switch set up like that... its a no no .. if you forgot and had it on during a pass it wont kill the ignition if needed and your knocked out EDIT I use to have a switch on the panel just to kill the alt during a pass but I seen ZERO difference in et or mph but that was with the output still on the battery side of the switch... so when I rewired the car I left that switch out of it Last edited by MR_P_BODY; 03/28/14 05:17 PM.

Re: Power Cut Off switch Question. [Re: MR_P_BODY] #1599667 03/28/14 05:22 PM 03/28/14 05:22 PM
Joined: Jan 2003 Posts: 27,421 Balt. Md 3 383man Too Many Posts
383man Too Many Posts 3 Joined: Jan 2003 Posts: 27,421 Balt. Md	Quote: Quote: Most I know do what Cab says and run the alt output wire to the battery side of the cutout switch. Another option is like I did years ago on my bracket car and that was I put a toggle switch on one of the field wires and ran it inside the car so I could kill the charging system when I made a pass and you can also just kill the charging circuit when going thru tech with that toggle switch in the car so it dies when the kill (cutout) switch is turned off. It is alot less wire to run if you just tap into a field wire and run it in the car within the drivers reach on a toggle switch. I burned out a rotor on my bracket cars alt so thats one reason I would kill the charging system when making a pass. Ron Dont let the tech guy see you with a separate switch set up like that... its a no no .. if you forgot and had it on during a pass it wont kill the ignition if needed and your knocked out I run the alt output wire to the battery side of the cutout switch on my 63. I also put a voltmeter in the car since the stock ammeter wont read correctly when you run the alt output wire like that. On my old 340 bracket car in the late 70's and early 80's I burnt out two alt rotors so I thought taken power away from the rotor on the 6500 rpm passes may help to not damage the alt rotor circuit. Did it help ?? Well it did not burn out any more alt rotors but I did roll the car about 1-1/2 years later. Course with the alt output killed the car will die when the cutout switched is turned off even if the alt is not wired right but like you said if you forget to hit the toggle switch and would crash then it wont kill the car so I do agree with NHRA on that rule that you still have to run the alt output wire correctly. Ron Last edited by 383man; 03/28/14 05:25 PM.

Re: Power Cut Off switch Question. [Re: 383man] #1599668 03/28/14 07:09 PM 03/28/14 07:09 PM
Joined: Oct 2010 Posts: 2,407 Ambridge, Pa. R rickraw top fuel
rickraw top fuel R Joined: Oct 2010 Posts: 2,407 Ambridge, Pa.	Does anyone have a fuse on their alt wire to the battery?

Re: Power Cut Off switch Question. [Re: rickraw] #1599669 03/28/14 07:28 PM 03/28/14 07:28 PM
Joined: Nov 2009 Posts: 3,410 Belpre,Ohio C CHAPPER master
CHAPPER master C Joined: Nov 2009 Posts: 3,410 Belpre,Ohio	Quote: Does anyone have a fuse on their alt wire to the battery? I do. If you like drag racing, support your local track.

Re: Power Cut Off switch Question. [Re: rickraw] #1599670 03/28/14 07:38 PM 03/28/14 07:38 PM
Joined: Jul 2004 Posts: 653 Fredericksburg Va P plycuda mopar
plycuda mopar P Joined: Jul 2004 Posts: 653 Fredericksburg Va	I have one on the alt and the starter wire

Re: Power Cut Off switch Question. [Re: CHAPPER] #1599671 03/28/14 08:03 PM 03/28/14 08:03 PM
Joined: Jul 2006 Posts: 4,319 Puyallup, WA S StealthWedge67 master
StealthWedge67 master S Joined: Jul 2006 Posts: 4,319 Puyallup, WA	Quote: Quote: Does anyone have a fuse on their alt wire to the battery? I do. Lets go over this.... What size fuse, and where exactly is it? LemonWedge - Street heavy / Strip ready - 11.07 @ 120

Re: Power Cut Off switch Question. [Re: StealthWedge67] #1599672 03/28/14 08:30 PM 03/28/14 08:30 PM
Joined: Jul 2004 Posts: 653 Fredericksburg Va P plycuda mopar
plycuda mopar P Joined: Jul 2004 Posts: 653 Fredericksburg Va	I have 150 and 300 amp 8092265-20140328_180958-Copy.jpg (170 downloads)

Re: Power Cut Off switch Question. [Re: StealthWedge67] #1599673 03/28/14 08:44 PM 03/28/14 08:44 PM
Joined: Jan 2003 Posts: 27,421 Balt. Md 3 383man Too Many Posts
383man Too Many Posts 3 Joined: Jan 2003 Posts: 27,421 Balt. Md	My original harness uses the fuseable links to protect the alt output wire from a short. I added a 70 amp large type bolt on fuse at the battery on my 63 with the battery in the trunk as it has eyelet terminals so I bolted it to the battery cable end and then bolted the wire from the alt to it as I put an eyelet terminal on the alt wire at the battery end. Ron Last edited by 383man; 03/28/14 09:00 PM.

Re: Power Cut Off switch Question. [Re: 383man] #1599674 03/28/14 10:07 PM 03/28/14 10:07 PM
Joined: Nov 2003 Posts: 10,384 Upstate NY Bigcube I Live Here
Bigcube I Live Here Joined: Nov 2003 Posts: 10,384 Upstate NY	I don't like running the alternator wire to the battery because that wire will be hot all the time. I set mine up with a relay. I use a continuous duty relay, similar to a Ford starter relay. See attachment. 8092372-2519432-KILLSWITCHRELAY.JPG (1966 downloads) Jim

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