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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:
though circling back from a safety perspective, is good to have disconnect of most of the electrical inside the car.
Agree.

This approach is a good solution for the S197, but will not work on the S550. On the S550 the starter cable is crimped to the Battery Junction Box cable at the battery terminal. Additionally, if you were to seperate these cables, the Alternator feeds into the BJB, so cutting power to the BJB would potentially result in Alternator/PCM power spikes.

Another title change ;)
 
Agree.

This approach is a good solution for the S197, but will not work on the S550. On the S550 the starter cable is crimped to the Battery Junction Box cable at the battery terminal. Additionally, if you were to seperate these cables, the Alternator feeds into the BJB, so cutting power to the BJB would potentially result in Alternator/PCM power spikes.

Another title change ;)

Won't it be easier to run a new wire from the alternator to the battery?
And then a new wire from the battery to the BJB that use a solenoid?
 
Won't it be easier to run a new wire from the alternator to the battery?
And then a new wire from the battery to the BJB that use a solenoid?
Maybe, But the S550 has a smart charging system that monitors current from the battery (via the negative terminal lead) and from the alternator at the BJB. At a minimum you'd have to relocate the current sensor and I'm not sure if there are other implications....
 
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Well, if your car is going up inflames and you hit the master electrical cutoff and it smokes the alternator, that's probably the least of your worries. In the "DoG" I ran an alternator switch so the alternator could be shut off during runs, stole this idea from drag racers, that way the master switch operates independently and doesn't kill the alternator, but the car still shuts off.
That being said, the current crop of cars are brutal on the electrics, with the fans, pumps and power assists all being electric.
 

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