The Mustang Forum for Track & Racing Enthusiasts

Taking your Mustang to an open track/HPDE event for the first time? Do you race competitively? This forum is for you! Log in to remove most ads.

  • Welcome to the Ford Mustang forum built for owners of the Mustang GT350, BOSS 302, GT500, and all other S550, S197, SN95, Fox Body and older Mustangs set up for open track days, road racing, and/or autocross. Join our forum, interact with others, share your build, and help us strengthen this community!

Nitpicked and Possibly NASA ST compliant s197 mustang engine cutoff circuit

OBLIGATORY DISCLAIMER: DO AT YOUR OWN RISK. I CANNOT BE HELD LIABLE FOR ANY LOSS OF LIFE, INCOME, RELATIONSHIP ISSUES, RUNNY NOSES OR LOSS OF PERCEIVED VALUE OF OPINION.

Parts list:

Cole Hersee 24106 12V Grounded Continuous Duty SPST Solenoid (amazon: https://www.amazon.com/gp/product/B001FQL43U/ref=oh_aui_search_detailpage?ie=UTF8&psc=1)

~16” prefabricated (or make your own) 4GA red power cable with 5/16” or 3/8” ring terminals

~10’ of 14-18ga hookup wire, ring terminals, inline fuse holder, grommets

1 SPST switch of your choosing

Option: 1 generic battery isolator switch (I bought this $8 one: https://www.amazon.com/Qiorange-Bat...845&sr=1-8&keywords=battery+disconnect+switch)

Option: rivnut tool to mount the solenoid, m6 bolts



Install:

Choose a mounting location for the solenoid. I had chosen the front of the passenger strut tower for proximity to the battery and the circuit I would be cutting off (the power feed to the smart junction box / fuse panel in engine bay). Drill holes and install riv nuts or bolts/lock washers/nuts/Loctite.


b781TlYl.jpg



On the battery, disconnect the negative cable and the power cable that routes to the fuse box. Install that cable on one end of the solenoid you just mounted. On the other main pole of the solenoid, install the 4GA power cable from the parts list and route/secure it and connect to the battery terminal so the circuit is so:

Battery positive terminal -> solenoid -> smart junction box

p0bVBq3l.jpg



Then find a suitable location for your switch(es). My car is setup with one switch on a radio delete panel, and another on the cowl panel where the windshield wipers are. There’s a good location (pictured) where the wiring won’t interfere with the operation of the wipers (if used).

Interior switch on console (with flipdown safety cover)
LrojhZMl.jpg
OrR9NcVl.jpg

cowl switch: (note, I had to move it slightly down from this picture to properly clear the hood, TEST FIT it before drilling)
3xd9rLxl.jpg


This circuit will look like this:

Battery positive terminal (use the small stud) -> 18ga wire (short) -> inline fuse holder (with 5a fuse) -> interior switch location -> exterior switch location (in series) -> solenoid



The solenoid body serves as its ground, so no need to run a separate ground wire unless you’re seeing issues with your mounted location or need to mount it to something other than the chassis.

Finally, cover any exposed wiring with boots and/or tape

By cutting off the SJB while running, the car won’t have power to its fuel system and ECU and this will effectively kill the motor. It’s not a true battery disconnect, however, that’s not what is required in the current rule sets for NASA.

Diagram:

GkkJTJvh.jpg


Finished Product:
rt8iEU4l.jpg
w3meRrEl.jpg


Caveats:

-Disconnecting the ECU can cause loss of learned parameters and stored diag codes

-if the fuse in the switched circuit fails, the power will fail across the board (by design, obviously)

I'll be adding pictures, having issues with previous hosting. Will edit soon.
 
Last edited:
Here's a list according to schematic of what the battery junction box provide power to and the fuse rating :

Smart Junction Box 80A
PCM Power 30A
Blower Motor 30A
Rear defrost 40A
Alternator 10A
Driver seat 30A
Passagenr seat 30A
Driver window 30A
Pass window 30A
Convertible top 40A
AC clutch 10A
Fuel pump 15A
ABS 40A + 30A
Wipper 30A
Fan 40A
Subwoofer 30A
 
The other relay I mentioned before handles 200A. I would be worried with a solid state relay since a common failure mode is shorted. Much more common than a properly sized mechanical relay, and they won't tolerate heat as well as the mechanical. If all the rules require is to kill power to the pump and ECU then you could get away with a smaller 2 pole NO relay on the output side of their individual fuses. Lots of ways you can do it.
 

Grant 302

basic and well known psychic
I don’t want anyone blowing up their cars following my lead :)

Nah. Anyone blowing up their car or frying their ECU takes responsibility for their own mistakes, right?

I was also wondering if the relay connection and vibration could be cause for your previous alternator issue?
 

captdistraction

GrumpyRacer
1,777
1,308
Phoenix, Az
Though in all fairness alternators are as sensitive a device as they get.

Some of the original requirements in crapcan endurance racing led a lot of teams to pop their alternators during inspections.

I just keep a fresh spare handy. Probably should upgrade the relay to the heavier piece mentioned and keep the existing one as a spare/backup




Sent from my iPhone using Tapatalk Pro
 
@captdistraction @ArizonaBOSS I'm in the process of researching this for my race car build. My interpretation is that NASA requires all power except fire system to be cut:

NASA CCR 15.8 "Master Switch An electrical master switch is required. It should be mounted so that it is easily accessible from the outside. If mounted outside the cockpit, it should be mounted in an area where it is least likely to be damaged (e.g. cowling near wipers). The switch should shut off the motor and cut all power except to the on-board fire system and any other life support / medical device. The switch location must be clearly marked with a “master switch cut-off decal."

I want to implement a low current solution with a center stack and cowl switch in series. However full electrical isolation has to deal with much higher current switching.

So far I'm at two options:

1) A solenoid in the main battery cable line -- this one handles 500 Amps: https://www.amazon.com/gp/product/B001YIPXR2/?tag=tmo302-20

or 2) A solid State device like this:
http://www.cartekmotorsport.com/Battery Isolator GT EN.pdf

The advantage of the solid state device is that it handles the risks associated with PCM and the Alternator (it cuts power to the PCM 0.5s before main power). The disadvantage is Cost, and that it will likely require re-work of the S550 current sensing in the negative battery cable. I'm also worried about the stated temperature rating of 85*.

The solenoid route is less expensive, but I'd have to figure out PCM and Alternator protection -- working on that....
 

ArizonaBOSS

Because racecar.
Moderator
8,539
2,368
Arizona, USA
@Black Boss That is the primary CC&R rule, but for the class we run (Super Touring), they only specify a kill switch, not a "full" battery disconnect. In the "Super Unlimited" class you need a true disconnect.

Check out the supplemental rules for the class you are interested in participating in to see what the minimum requirement is. HOWEVER--if you go the full isolator/disconnect route, you will be compliant in all cases.

Edit: That Cartek system looks good and I have seen that advertised before.
 
Last edited:

captdistraction

GrumpyRacer
1,777
1,308
Phoenix, Az
Run the other model solenoid mentioned (24213: its 4 post, but should be clear what the 2nd small post is clear). Use some rubber washers under it if you like (as long as there's a good ground contact).

I haven't had a problem using the solenoid. Battery drain is something to consider but i run a lithium polymer battery anyways; so I've learned not to leave it on for periods of time (and have a jump pack now, which I feel is a track day necessity for a dedicated racecar).

I edited the title to NASA ST2 since that's the specific ruleset I built this under.


Though I've been more wrong than right lately, if building a true total disconnect, make sure you give the alternator somewhere to dump remaining voltage into upon disconnect.
 
@ArizonaBOSS I just looked at: NASA Super Touring (ST & SU) Rules 2017 v11.5, section 7.2 for ST1-4:

7.2 NASA CCR Section 15 and 18 Exceptions All rules in Section 15 and 18 of the NASA CCR shall apply, with the following exceptions that shall supersede those in the CCR: CCR 15.6—Roll cages may be built to provide an unlimited amount of chassis stiffening. Any number of cage mounting points may be used above the six (6) minimum requirement, and, any number of additional tubes may be used above the minimum with additional attachment points to the body, including tubes that penetrate the firewall. CCR 15.8—An electrical master cut-off switch is required.

Am I missing something?
 
I think alternator issues are not a problem with this setup. You are not completely cutting off the alternator which is actually more dangerous for the PCM and other electronics. Alternator can still dump into battery when shut off and your are cutting out the electronics. FWIW, I could be dead wrong.

Also, capacity wise, this could be a problem for DD cars. But I don't have 3/4 of the fuses in the main box going to anything. No blower, rear defroster, windows, anything beyond what's necessary for driving the car really. So, for DD, get a larger one. I personally have heard of too many problems with SS ones lighting on fire.
 

captdistraction

GrumpyRacer
1,777
1,308
Phoenix, Az
I think alternator issues are not a problem with this setup. You are not completely cutting off the alternator which is actually more dangerous for the PCM and other electronics. Alternator can still dump into battery when shut off and your are cutting out the electronics. FWIW, I could be dead wrong.

Also, capacity wise, this could be a problem for DD cars. But I don't have 3/4 of the fuses in the main box going to anything. No blower, rear defroster, windows, anything beyond what's necessary for driving the car really. So, for DD, get a larger one. I personally have heard of too many problems with SS ones lighting on fire.

If starting from scratch I'd get the bigger one just in case. While I haven't had an issue, its only $10 or so more for the larger solenoid which in theory would have a longer service life.

I meant a direct battery cutoff as being a problem with alternators (where you end up separating the battery from everything and the alternator either backfeeds or causes other issues). This setup is alternator safe (though it was mentioned earlier that there could be some corrolation between issues with the alternator and the solenoid, though I'm not convinced they were related)

Best advice is to take this by the local tech inspectors for whatever series you are going to run and get their OK before proceeding.
 
If starting from scratch I'd get the bigger one just in case. While I haven't had an issue, its only $10 or so more for the larger solenoid which in theory would have a longer service life.

I meant a direct battery cutoff as being a problem with alternators (where you end up separating the battery from everything and the alternator either backfeeds or causes other issues). This setup is alternator safe (though it was mentioned earlier that there could be some corrolation between issues with the alternator and the solenoid, though I'm not convinced they were related)

Best advice is to take this by the local tech inspectors for whatever series you are going to run and get their OK before proceeding.
I completely agree. A full cutoff would require an alternator cutoff with grounded resistor. This setup is just fine. I think alternators on race cars are expendable items (albeit last for quite a while, comparatively). They sure as hell are cheaper than brakes or tires.
 

ArizonaBOSS

Because racecar.
Moderator
8,539
2,368
Arizona, USA
@ArizonaBOSS I just looked at: NASA Super Touring (ST & SU) Rules 2017 v11.5, section 7.2 for ST1-4:

7.2 NASA CCR Section 15 and 18 Exceptions All rules in Section 15 and 18 of the NASA CCR shall apply, with the following exceptions that shall supersede those in the CCR: CCR 15.6—Roll cages may be built to provide an unlimited amount of chassis stiffening. Any number of cage mounting points may be used above the six (6) minimum requirement, and, any number of additional tubes may be used above the minimum with additional attachment points to the body, including tubes that penetrate the firewall. CCR 15.8—An electrical master cut-off switch is required.

Am I missing something?
It's a matter of definition (and to some degree, interpretation), but an electrical master cut-off switch is not the same thing as a battery isolator or battery disconnect.
Definition of "Electrical Master Cutoff Switch" in NASA Primary CC&R:
dERWCuP.png

I was going to reference the difference for a specific battery disconnect clause in the Super Unlimited rules, but those were apparently updated to show "Electrical Master Cutoff Switch" same as I have noted above.

The test for functionality of the kill switch / electrical master cutoff switch is as follows (your tech inspector may vary--but this is what AZ region does, advise consulting with your region's inspector to be safe):
Power on vehicle.
Start vehicle.
With vehicle running in neutral, rev to 3000 RPM and hold.
While holding at 3000 RPM, trigger kill/cutoff switch.
Success criteria: Vehicle should cease running immediately.

The way @captdistraction and I have it rigged up is that it stops all battery power flow from the battery + terminal before it hits the engine bay power distribution box. That kills the PCM and all vehicle electrical functions. Agreed it is not the same thing as a battery disconnect/isolator but it does meet the letter and spirit of the rules.

Also--so far no issues with battery drainage like this. Typically I leave the master-switch active in-between sessions at the track, but shut it off each night at the track. Also my car lives on a battery tender when it is at home in the garage. I am using a lightweight Odyssey PC680 battery (not as extreme as Capt's Battery Tender Lithium one).
One time I did kill one of these batteries when I forgot to kill the main power after I loaded the car into the trailer; it sat for about 18 hours without running. Fortunately, this was on the way back home FROM the track.
 

TMO Supporting Vendors

Top