S&S Diversified: Prototype CAD CAM Design Fabrication Machining Technical - Northeast NY NJ CT PA NYC
  Prototype Design & Engineering
Concept to Delivery: S&S is your "one-stop" vendor.		 3D Modeling CAD Drawing & Plotting
CAD Technical CAD Drawing and 3D Modeling with Multi-color Pen Plotting.		 Prototypes & Fabrication
Turn, Mill, Drill, Cut, Weld, Paint, Create. S&S fabricates your Prototype.		 Vintage, SCCA, and custom Auto & Motorsport
SCCA Race Car, Motorsport Preperation, Tuning.		 HTML coding and Web Design
S&S can put your business on the web
 
Master "Kill" Switch Wiring for SCCA Race Cars with Alternators

This all started back in 1998 or so when my BMW 2002 was still running Improved Touring, and suddenly the then "Denver" powers-that-be mandated all cars shalt haveth a kill switch.

Well, fine and dandy. I had a few of the simple BIG RED SWITCH things laying around, but I remember the expensive and horrible results when I tried to install one of these on my '85 MR2 [footnote: The "Lizzy B" ex. T. Lynch and ex. J. DeLuca racing MR2!] . . . anyway, I let the smoke out of some important innner alternator osilfrometer thingies, which was discovered at the racetrack with a dying battery, weak fuel injection, and poor ignition. And Toyota alternator internal domilflachys are NOT cheap. SO... Along comes Bill Hughes, famed NNJR region Tech Inspector Scrutineering Person, and thus is born an article that guides us poor alternator-saddled folks with wiring the special kill switch needed for SCCA racing. Be cause as we all know, REAL race cars don't need no stinkin' alternators. [cough...]

Note that my original "MR2" method WILL work, if you isolate the D+ heavy alternator wire, but the only problem is it will likely ruin your alternator if you ever use it. But it WILL kill every circuit on the car, and it does meet the GCR. The GCR is simply concerned with shutting down your car instantly, they really don't care if you ruin your alternator.

But for us shoestring guys, even though everything only costs $50 . . . I'd like to keep my alternator healthy. Plus, I've noticed that ONE BIG RED SWITCH is really nice to shut off and make CERTAIN that nothing is left on - no pumps, lights, radios, cigar lighters, neon underbody accents, blue LED winshield washer spray nozzles, subwoofer amps, DVD navigation systems, etc etc etc . . . you know, those race car things that get left on over the winter and make you rush out buy a new battery the early Spring night before a race!

I really check and test everything I do. However, do this modification at your own peril. I cannot be responsible for your warranty, mojo, hair loss, law enforcement woes, mortgage rate, Viagra supply, or anything else that might and/or might not befall you. For off-road non-CARB vehicles, as far as I know. Canadian and French vehicles are probably different, if anyone cared. This information is gladly provided for educational purposes only. Your mileage may vary. Yadda yadda yadda...

TECHNOTES -- ARTICLE 01:
WIRING YOUR MASTER SWITCH (for cars with alternators)
By: Bill Hughes -- NNJR Tech Chief   11 Jan 1998
Edited and Illustrated circa 1998-2003 by Steve McChesney, BSEE

 Now for IT drivers, a master switch is required this year. This switch must kill all power except for an electrically operated fire system, if so equipped. This switch must also shut the motor off, which means that you will need a 3 pole switch, not a single pole. If a single pole is used, two things will happen: 1) The car will keep running because of residual magnetism in the alternator, which will keep the alternator supplying power, and 2) the field being disconnected on the alternator will cause the smoke to leak out of your diodes, (and since we all know that electronics runs on smoke, the depletion of this smoke will render the alternator inoperative).

The mounting location for this switch is just in front of the windshield on either side of the car, below the center of the rear window, or mounted on a bracket attached to the roll cage (with the bracket welded or clamped to the bar, no bolts into the cage) in a position easily accessible from the open window. Don't forget your "OFF" decal.

The easiest way to wire an OMP 3 Pole switch, (available at Driving Impressions), on most cars is as follows: Remove the battery ground, then disconnect the positive battery cable from the starter. This will be connected to one of the large terminals on the switch. Find the smaller auxiliary lead on the positive battery cable near the battery terminal and cut it off close to the cable. This lead will be connected to the second large terminal of the switch. Attach another battery cable to this second terminal and run this cable to the starter. Most auto parts stores will make this cable up for you, just let them know how long you need it and what size studs each end attaches to. Also, from the same terminal, run a 12 gauge wire to one of the terminals marked "1" on the bottom of the switch. The two terminals marked "1" are the Normally Closed contacts of the switch. The other "1" terminal will be connected to the supplied resistor. The other side of this resistor is connected to a good ground. This resistor is what protects your alternator diodes. The resistor should be tie wrapped to the other wires and the leads insulated. You have now succeeded in disconnecting your battery and protecting your alternator, now for shutting off your motor. There are two terminals left on the switch, these are marked "2". These terminals are for the Normally Open contacts of the switch. Disconnect the wire going to the "+" terminal of your ignition coil and attach this to one of the terminals marked "2". Run a 12 gauge wire from the remaining "2" terminal to the ignition coil "+" terminal. Now all that is left to do is to mount the switch and reconnect your battery ground cable.

After installing, start the car and make sure the switch will shut it off. With the switch off, check to make sure that the car will not crank, the fuel pump, wipers, and all lights will not operate.


Steve adds: Here's an illustration to make the muddy waters perfectly opaque:


The resistor is a ballast-type ignition resistor, and almost any rating from 3 to 15 ohms will work, provided it can handle 10-20 watts. The resistor should come with the cut-off master switch if you get the right one. Pegasus and Racer's Wholesale both carry these switches as complete kits. Calterm, OMP, and Hella are brands that I've used and respect.

Note that "EARTH" means the chassis, or frame ground in this case. You do not have to drive a copper rod into the Earth and hook that to your racecar. Because that would be really incovenient, and the wire would have to be fairly long and get all tangled and twisted as you went round and round the racetrack...


 

Here's an in-depth article I blatently lifted from the Mumm Brothers Racing website. This covers various wiring schemes that have been used on Spec Racer Renaults for cut-off switches. Note that some of these [e.g. Style #1] probably are not even SCCA legal at this point, considering that they will not kill the engine - kinda the whole point of the exercise. Bill Hughes' solution most closely resembles "Wiring Style #2". I've included this article here as some background for those of you [me] that obsess about these kinds of things. Have a look if you dare, and for Spec Racer folks, please check out the Mumm's website for some great SRF hints.


LINK to Mumm Brothers Racing: Spec Racer Secrets

 Master Switch Wiring

Background
There have been at least 4 variations of wiring for the master switch on the SRF.   In this article, I’ll review all 4 and present the pro’s and con’s of each.
 
  Wiring Style #1
This is the original wiring for the first 33 cars that were at the Runoffs in 1993.
  .master1.gif (11696 bytes)
  Pro’s Con’s
  - No parts of the car are “hot” with the master switch off.
- Zero current drain when the master switch is off.
- Engine does not shut off when the master switch is opened.
- Fault codes are not retained after the master switch is opened.
- EEC “learned” information is lost when the master switch is opened.
 
  Wiring Style #2
  Same as wiring style #1, but with a shorting resistor added to kill the alternator output when the master switch is opened -- thereby stopping the engine.
  master2.gif (11935 bytes)
  Pro’s Con’s
  - No parts of the car are “hot” with the master switch off.
- Zero current drain when the master switch is off.
- Engine shut off when the master switch is opened depends on the integrity of the shorting resistor and its wiring.
- Fault codes are not retained after the master switch is opened.
- EEC “learned” information is lost when the master switch is opened.
 
  Wiring Style #3
  Some significant changes here.  This diagram appeared in  the 2/17/94 update from Roush to SCCA Enterprises.  In this wiring style, the power to the ignition switch is taken through the normally open auxiliary contacts of the master switch.  Opening the master switch (putting it in the “normal” position), disconnects the battery from the alternator and the starter and --via the auxiliary contacts --- the alternator is disconnected from the ignition switch.  The tape-wrapped EEC power wire remains connected to the battery at all times.  This is the way my car is wired.
  master3.gif (11561 bytes)
  Pro’s Con’s
  - Fault codes are retained after the master switch is opened.
- EEC “learned” information is saved when the master switch is opened.		 - EEC is “hot” at all times the battery is connected.
- Clearing Fault codes requires disconnecting the battery.
- EEC draws some (very small) current at all times
 
  Wiring Style #4
  This is the current “Green Book” wiring scheme.
  master4.gif (11775 bytes)
  Pro’s Con’s
  - Zero current drain when the master switch is off. - Alternator is “hot” at all times the battery is connected.
- Fault codes are not retained after the master switch is opened.
- EEC “learned” information is lost when the master switch is opened.
 

Rev. 3/14/98




  Feedback
  I welcome your comments or ideas on this information.  Feel free to drop me a line via “Comments for the Bro’s”.   -Barry

 
LINK to Mumm Brothers Racing: Spec Racer Secrets
 
END OF EXCERPTS



Hope that helps. This is a 90 minute, "four beer" kind of job. Pretty rewarding if you're not real comfortable with this kind of mod, but want to get your hands dirty.

Best wishes, S.A. McChesney aka "SteveRacer"

11/6/03         (C) 2003 S&S Diversified

    Feel free to Link !