HELP with Master Cut Off Switch
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From: Beverly NJ
HELP with Master Cut Off Switch I have a "79" Camaro with an LS1. My problem is with the Master Cutt Off Switch. I have tryed everything and can not get the car to shut off after hitting the switch. If I hit the switch and pull the ALT. plug then the car will die and if I hit the switch while the car is off, all power is cut off, it just won't cut the power while car is running. Any help or ideas would be Appriciated. 
Joined: Sep 2004
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From: Downers Grove, IL
The easiest way to fix this is to use a switch that also has contacts to route the alternator power through it. Which style switch do you have? Is it one with a linkage rod or does it just have a **** on it?
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From: Beverly NJ
It has the rod it's a Cole Hersee. It has batt in batt out,alt in alt out.I installed just the batt side, and batt and alt side still will not kill car. This is the only problem with the car. And i don't want to put the batt under the hood.
Joined: Sep 2004
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From: Downers Grove, IL
So your switch has the second set of contacts to hook the alt too? You just hooked up the main battery cable to the switch right? You also need to hook up the alt, I would cut the little red wire that goes to the 4 pin weatherpack connector on the alt and extend that wire so that it goes through the second set of contacts on the switch. That way when you turn the switch off the battery and alternator will both be disconnected.
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From: Pittsburgh, PA
when you hit the switch, you are killing the battery, but the car is still running on the alternator. You have to run the big wire from your alternator to the kill switch. My battery is in my trunk and I had to do the same thing.
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From: Lake Zurich, IL
curious... with this would it also be possible to use a relay to kill the Power to the PCM?
Battery -> Kill
Kill -> give + to rest of car
off the Kill have a relay ... when power, supply power to PCM, but when no power, kill power to PCM
That should cause the injectors to stop firing, spark from sparking, etc....
prolly not track legal though?
Battery -> Kill
Kill -> give + to rest of car
off the Kill have a relay ... when power, supply power to PCM, but when no power, kill power to PCM
That should cause the injectors to stop firing, spark from sparking, etc....
prolly not track legal though?
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Teching In
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From: Beverly NJ
I have the switch wired correctly the problem is with the wire that comes from the PCM to the alt. When you hit the switch car still runs ,Hit switch and pull weathepack connector on alt car will die.
TECH Resident
Joined: May 2004
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From: SoCal
Doesn't the PCM require a constant 12V supply to keep from going through re-learn? Perhaps the schematic doesn't show it, but isn't a low current fused supply is required to the PCM?
Got another question, which hopefully doesn't derail this thread. Does Chevy use an inertia fuel pump cut off like Ford does? I've never seen it mentioned. I would think it's an important safety device worth having in case of accident.
Thanks,
Andy1
Got another question, which hopefully doesn't derail this thread. Does Chevy use an inertia fuel pump cut off like Ford does? I've never seen it mentioned. I would think it's an important safety device worth having in case of accident.
Thanks,
Andy1
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From: Beverly NJ
You have a red 12v key crank run.
Orange goes to positve side of battery or starter
the wire I am talking about is the wire that comes from pin 15 from the computer to the L terminal on the alt.
Orange goes to positve side of battery or starter
the wire I am talking about is the wire that comes from pin 15 from the computer to the L terminal on the alt.
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From: Downers Grove, IL
Originally Posted by 79camarols1
Are you talking about the wire that comes from the PCM to theweatherpack. I have two wires on the alt they are batt to the output lug and the PCM wire to the L[AKA B] terminal.
Yes, if you have a switch like thishttp://www.flamingriver.com/index.cf...prod/prd64.htm
wher it has 4 contacts I would wire the wire from the PCM to the alt L terminal to the little contacts. Cut the wire between the PCM and the alt and extend it back to the contacts.
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From: Downers Grove, IL
Heres a couple of diagrams that will hopefully help clear everything up. Thank You to Born-again 7 for posting the first one, as you can see I borrowed it since my paint skills are horrible, I hope I didn`t butcher it too much.
This is the only solution that I know of if you have a switch with only 2 posts. It should pass tech, but I don`t know if it is 100% legal though since I think the rule says the switch must cut all electrical power and when you wire it this way the switch does not cut power to the alternator.
I have seen some 4 post switches say that you should wire the small posts between the alt and the battery like in the diagram above. This will cut the power to everything, but it can damage the alternator. If the car is running and you turn the disconnect off the alternator sensing wire (the wire between terminal L on the alt and the PCM) sees that the system voltage is dropping and tells the alt to produce more voltage. Since the output of the alternator is not connected to anything the sensing wire still sees the voltage as dropping and trys to up the output voltage even more. That goes on and on and the output voltage of the alternator can spike to above 50V and kill the voltage regulator. So I would not wire the alt like that
.
This is how I would wire the alternator. If you use a 4 pole switch you can wire the large poles to cut battery power and then use the small poles to cut the connection between the alt and the PCM so that all of the power to the vehicle is cut and the engine shuts down immediately.
This is the only solution that I know of if you have a switch with only 2 posts. It should pass tech, but I don`t know if it is 100% legal though since I think the rule says the switch must cut all electrical power and when you wire it this way the switch does not cut power to the alternator.
I have seen some 4 post switches say that you should wire the small posts between the alt and the battery like in the diagram above. This will cut the power to everything, but it can damage the alternator. If the car is running and you turn the disconnect off the alternator sensing wire (the wire between terminal L on the alt and the PCM) sees that the system voltage is dropping and tells the alt to produce more voltage. Since the output of the alternator is not connected to anything the sensing wire still sees the voltage as dropping and trys to up the output voltage even more. That goes on and on and the output voltage of the alternator can spike to above 50V and kill the voltage regulator. So I would not wire the alt like that
. This is how I would wire the alternator. If you use a 4 pole switch you can wire the large poles to cut battery power and then use the small poles to cut the connection between the alt and the PCM so that all of the power to the vehicle is cut and the engine shuts down immediately.
Joined: Sep 2004
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From: Downers Grove, IL
Originally Posted by horist
curious... with this would it also be possible to use a relay to kill the Power to the PCM?
Battery -> Kill
Kill -> give + to rest of car
off the Kill have a relay ... when power, supply power to PCM, but when no power, kill power to PCM
That should cause the injectors to stop firing, spark from sparking, etc....
prolly not track legal though?
Battery -> Kill
Kill -> give + to rest of car
off the Kill have a relay ... when power, supply power to PCM, but when no power, kill power to PCM
That should cause the injectors to stop firing, spark from sparking, etc....
prolly not track legal though?
