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Thread: master switch

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    Senior Member cliff's Avatar
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    Default master switch

    Hoping for some input here. Piper/Honda and i have been using the traditional Pegasus master switch for years without much issue.
    This is the master switch with the alternator protection set up with the added spades on the bottom. I switched to a more traditional Bosch switch as i had a couple of incidents where the master switch just shut off...lastest batch seemed less confidence inspiring relative to just turning off after a bounce or vibration or whatever. Anyway, all wired up, run the car, and then turn off the car via the master switch, it keeps running. Car will turn off at this point with the ignition switch. There still "connectivity" between the two lugs on the master switch after turning off. Walk away, come back in 4 or 5 minutes there is now no connectivity between the two lugs. I actually drove a lap with master switch off just to see what would happen. It ran but was acting like it was about ready to stop. So...I assume the alternator is still "hot" after the master switch is off. The Pegasus switch is plastic and you could argue that it is isolated from the chassis...the Bosch switch is metal,,,metal frame, metal nuts and bolts holding it. I have not tried (yet) to isolate the Bosch switch from the frame. Anyone have any thoughts as to what is going on here...? Please and Thank You!

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    Senior Member John LaRue's Avatar
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    Cliff - Do you have the master wired in on the ground or power side? Lathrop always had us install the master on the ground side.

    A couple of things I am sure you have thought about:

    -Confirm that if you disconnect the cables to the master there is no power.

    -Try removing the master from the chassis to confirm your suspicions about conductivity.

    There was a master switch issue at Pitt with an FA car so there might be a product problem.

    Good luck,

    John

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    Honestly I don't know why people still use those hella type switches. I've seen so many problems with them yet they're still in use. I use aircraft switches/breakers for all critical components. I have a 20 amp breaker on the roll bar that feeds a second one on the dash that provides power to the ECU and fuel pump switch which is another breaker. My voltage regulator output is wired directly to the battery and starter current goes from the battery to a very short cable to the starter solenoid which is located a few inches away. Lots of people think starter current has to go through the roll bar switch but it doesn't. The roll bar switch only has to shut the car off, thats the only requirement.

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    Contributing Member lowside67's Avatar
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    Quote Originally Posted by 10rmotor View Post
    Honestly I don't know why people still use those hella type switches. I've seen so many problems with them yet they're still in use. I use aircraft switches/breakers for all critical components. I have a 20 amp breaker on the roll bar that feeds a second one on the dash that provides power to the ECU and fuel pump switch which is another breaker. My voltage regulator output is wired directly to the battery and starter current goes from the battery to a very short cable to the starter solenoid which is located a few inches away. Lots of people think starter current has to go through the roll bar switch but it doesn't. The roll bar switch only has to shut the car off, thats the only requirement.
    I don't think that is a correct interpretation. Here is the relevant GCR:

    9.3.35. MASTER SWITCH
    All cars, except Touring, B-Spec and C-Spec, shall be equipped with a master switch easily accessible from outside the car. Spec Racer Fords (SRF/SRF3) shall be wired per RFSRII. The master switch shall be installed directly in either battery cable and shall cut all electrical circuits but not an on-board fire system. All terminals of the master switch shall be insulated to prevent shorting out. It shall be clearly marked by the international marking of a spark in a blue triangle and mounted in a standard location. Off position shall be clearly indicated at the master switch location.
    If I am reading your post correctly, you have an aircraft style circuit breaker mounted at the rollbar which is your actual "disconnect" device? If I was a tech inspector, I'd ask myself if that meets the definition of a "master switch" but that one could probably be argued and end at a stalemate.

    The bigger and much more obvious problem is that the rule very clearly says the master switch must cut ALL electrical circuits. In your description, the connection between your battery and starter is a circuit that is not cut when the switch is activated. In this way, I think it is objective that your design does not meet the GCR.

    Personally I installed the same TE high current remote relay that many professional cars use - it's low cost, does not require physically routing battery cables all the way to/from the rollbar, but cuts all connection between the battery and the rest of the car when not activated.

    -Mark
    Mark Uhlmann
    Vancouver, Canada
    '12 Stohr WF1

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    Quote Originally Posted by lowside67 View Post
    I don't think that is a correct interpretation. Here is the relevant GCR:



    If I am reading your post correctly, you have an aircraft style circuit breaker mounted at the rollbar which is your actual "disconnect" device? If I was a tech inspector, I'd ask myself if that meets the definition of a "master switch" but that one could probably be argued and end at a stalemate.

    The bigger and much more obvious problem is that the rule very clearly says the master switch must cut ALL electrical circuits. In your description, the connection between your battery and starter is a circuit that is not cut when the switch is activated. In this way, I think it is objective that your design does not meet the GCR.

    Personally I installed the same TE high current remote relay that many professional cars use - it's low cost, does not require physically routing battery cables all the way to/from the rollbar, but cuts all connection between the battery and the rest of the car when not activated.

    -Mark
    Thats where everyone gets tripped up. So cut every electrical circuit? So in between the fuel pump, brake light, rain light, low oil pressure light, data system, electrical gauges, etc? Thats obviously not possible or the intent and from a reliability standpoint a huge failure waiting to happen. But what it does do is cut off electrical power to all circuits. Just like your relay does. I'd argue that your system isn't in compliance as the circuit that toggles your relay has to be energized at all times! It is a grey area with respect to how I wire the regulator output as the regulator is directly connected to the battery but if the engine stops running (ECU power shut off) that circuit is dead as well, so the master switch has done its job.

    From a safety standpoint, I'd argue that my system using #12 wire is safer than a #8 wire going from the battery to the roll bar as the smaller gauge wire can carry less amperage and in the event of a short create less of a fire hazard than the larger #8.

    Multiple cars over almost 30 years including runoffs of using these breaker switches and not one tech inspector has had a problem with them. If they did, then they'd have to specify a certain switch to be used, as well as a sample wiring diagram. I'm obviously disregarding any SRF considerations here.

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    Contributing Member lowside67's Avatar
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    Quote Originally Posted by 10rmotor View Post
    Thats where everyone gets tripped up. So cut every electrical circuit? So in between the fuel pump, brake light, rain light, low oil pressure light, data system, electrical gauges, etc? Thats obviously not possible or the intent and from a reliability standpoint a huge failure waiting to happen. But what it does do is cut off electrical power to all circuits.
    We are 100% agreed that the master switch is clearly not intended to physically interrupt every leg of every circuit, instead that "cut" means in this context that there's no longer a complete path from the battery to the end device.

    However, your system does not cut off electrical power to all circuits. It cuts off electrical power to all circuits except the starter solenoid which continues to have a direct connection to both battery and ground regardless of what position your "switch" is in. For that reason, I maintain that it is not compliant.

    It's a small distinction and I am not at all surprised that tech inspectors might not flag it over time, but I think it's worth at least highlighting the risk to others who may follow your advice and run into a tech inspector that does not see it the same way.

    -Mark
    Mark Uhlmann
    Vancouver, Canada
    '12 Stohr WF1

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    Senior Member John LaRue's Avatar
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    If you want to debate/discuss various wiring ideas create another thread. This should be focused upon responding to Cliff's question.

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    Quote Originally Posted by lowside67 View Post
    We are 100% agreed that the master switch is clearly not intended to physically interrupt every leg of every circuit, instead that "cut" means in this context that there's no longer a complete path from the battery to the end device.

    However, your system does not cut off electrical power to all circuits. It cuts off electrical power to all circuits except the starter solenoid which continues to have a direct connection to both battery and ground regardless of what position your "switch" is in. For that reason, I maintain that it is not compliant.

    It's a small distinction and I am not at all surprised that tech inspectors might not flag it over time, but I think it's worth at least highlighting the risk to others who may follow your advice and run into a tech inspector that does not see it the same way.

    -Mark

    Depends on how you define cut power, doesn't it? Your redefinition says exactly the way I interpreted it earlier, i.e. the switch is in the way of the current path from battery to Power of every circuit. Electrical current cannot get to the solenoid to actuate it, so the circuit does have electrical power cut. Since we agree that the master isn't intended to interrupt every circuit, and the GCR doesn't say specifically the switch needs to interrupt starter current I believe I'm compliant. From a safety standpoint I'm better as I have maybe six inches of main cable to starter solenoid, vs four plus feet from battery to a roll bar mounted switch.

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    Senior Member David Clubine's Avatar
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    Quote Originally Posted by cliff View Post
    Hoping for some input here. Piper/Honda and i have been using the traditional Pegasus master switch for years without much issue.
    This is the master switch with the alternator protection set up with the added spades on the bottom. I switched to a more traditional Bosch switch as i had a couple of incidents where the master switch just shut off...lastest batch seemed less confidence inspiring relative to just turning off after a bounce or vibration or whatever. Anyway, all wired up, run the car, and then turn off the car via the master switch, it keeps running. Car will turn off at this point with the ignition switch. There still "connectivity" between the two lugs on the master switch after turning off. Walk away, come back in 4 or 5 minutes there is now no connectivity between the two lugs. I actually drove a lap with master switch off just to see what would happen. It ran but was acting like it was about ready to stop. So...I assume the alternator is still "hot" after the master switch is off. The Pegasus switch is plastic and you could argue that it is isolated from the chassis...the Bosch switch is metal,,,metal frame, metal nuts and bolts holding it. I have not tried (yet) to isolate the Bosch switch from the frame. Anyone have any thoughts as to what is going on here...? Please and Thank You!

    Cliff, I assume the bosch switch still has the 4 terminals on the bottom?

    David

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    Senior Member cliff's Avatar
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    David
    no it does not...Per Doug Jr i connected the two Z wires together, got rid of the ground with the resistor and the 4th was a line going from one of the "W" tangs to the hot lug. Longer story, i set up an old style, with these bottom tangs, after the Bosch switch as an exercise and that did not solve the problem. So, in essence, i ran it the old way with all of the z-wires attached appropriately, and the resistor and the other one going to the "hot when turned on" lug, and it still ran with said Bosch unit before the old style. The bosch is bolted to the frame, not isolated, if that has anything to do with it. It seems obvious to dummy me that the alternator is sending power backwards up to the master switch thru the 4 gauge wire after the master switch is turned of...meaning it is still hot, until it is not.

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    Senior Member David Clubine's Avatar
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    Quote Originally Posted by cliff View Post
    David
    no it does not...Per Doug Jr i connected the two Z wires together, got rid of the ground with the resistor and the 4th was a line going from one of the "W" tangs to the hot lug. Longer story, i set up an old style, with these bottom tangs, after the Bosch switch as an exercise and that did not solve the problem. So, in essence, i ran it the old way with all of the z-wires attached appropriately, and the resistor and the other one going to the "hot when turned on" lug, and it still ran with said Bosch unit before the old style. The bosch is bolted to the frame, not isolated, if that has anything to do with it. It seems obvious to dummy me that the alternator is sending power backwards up to the master switch thru the 4 gauge wire after the master switch is turned of...meaning it is still hot, until it is not.
    I didn't know that it could be wired this way.

  13. #12
    Senior Member cliff's Avatar
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    well maybe it can't...thus the issue...

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    Contributing Member problemchild's Avatar
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    Quote Originally Posted by cliff View Post
    well maybe it can't...thus the issue...
    Perhaps you should just follow the HPD specs but replace the switch more often. Since I moved my switches from the metal chassis mount to a softer fibreglass panel mount, I do not recall losing a switch, and it has easier access.
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