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Battery cutoff switch and msd, car wont die
#1478075
08/01/13 09:31 PM
08/01/13 09:31 PM
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Joined: Aug 2003
Posts: 1,062
Amherst,NY
challengermike
OP
super stock
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OP
super stock
Joined: Aug 2003
Posts: 1,062
Amherst,NY
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How do you wire an msd box with a battery cut off switch and have the car shut off when the cutoff switch is flipped off. When I bought the car the msd box heavy red wire was hooked to the back of the alternator and the cutoff switch would kill the car. The msd instructions say not to hook it to the alt, I figured that is why the original box I had died. So I wired it to the off/ disconnected side of the cutoff switch and the switch wont kill the car. My car doesn't have the stock wiring but it is wired battery to the cutoff switch and everything comes off of the disconnect side of the cutoff switch. Any ideas would be great. I have tried msd's instructions of using a 4 pin ballast resister on the small red wire on the box and it didn't help. I also tried the msd's big wire to the battery directly and it did help. Im just afraid to rewire it to the back of the alt and have another box fail. If it matter's its a 2 pole cutoff switch.
Last edited by challengermike; 08/01/13 09:32 PM.
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Re: Battery cutoff switch and msd, car wont die
[Re: Jeepmon]
#1478079
08/01/13 10:51 PM
08/01/13 10:51 PM
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Joined: Aug 2003
Posts: 1,062
Amherst,NY
challengermike
OP
super stock
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OP
super stock
Joined: Aug 2003
Posts: 1,062
Amherst,NY
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I have tried both sides of the cutoff switch and it wont die. The alt is hooked to the disconnect side. Are you saying the alt should be wired to the battery side of the switch? I thought the cutoff switch should kill all power to the car.
Last edited by challengermike; 08/01/13 10:54 PM.
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Re: Battery cutoff switch and msd, car wont die
[Re: challengermike]
#1478081
08/02/13 12:36 AM
08/02/13 12:36 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
I have tried both sides of the cutoff switch and it wont die. The alt is hooked to the disconnect side. Are you saying the alt should be wired to the battery side of the switch? I thought the cutoff switch should kill all power to the car.
All that switch is doing is cutting the battery source...
just like if you disconnect the battery in a production
car.. it continues to run... the big alt wire need
to go to the master shut off on the battery side of
the switch
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Re: Battery cutoff switch and msd, car wont die
[Re: MR_P_BODY]
#1478082
08/02/13 01:10 AM
08/02/13 01:10 AM
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Joined: Nov 2004
Posts: 8,094
Sunnyvale, CA
Jeepmon
master
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master
Joined: Nov 2004
Posts: 8,094
Sunnyvale, CA
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Quote:
Quote:
I have tried both sides of the cutoff switch and it wont die. The alt is hooked to the disconnect side. Are you saying the alt should be wired to the battery side of the switch? I thought the cutoff switch should kill all power to the car.
All that switch is doing is cutting the battery source...
just like if you disconnect the battery in a production
car.. it continues to run... the big alt wire need
to go to the master shut off on the battery side of
the switch
x2
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Re: Battery cutoff switch and msd, car wont die
[Re: challengermike]
#1478086
08/02/13 07:47 PM
08/02/13 07:47 PM
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Joined: Nov 2004
Posts: 8,094
Sunnyvale, CA
Jeepmon
master
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master
Joined: Nov 2004
Posts: 8,094
Sunnyvale, CA
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Quote:
What gauge wire should I run for the alt, Its a 120 amp cs130. Right now its hooked to my starter wire which is huge.
This is the tricky part.. per the spec's on a 120 amp alt, you need some stupid size wire like 4 gauge... but it will (almost) never be putting out a solid 120 amps..
So the simple answer will be the bigger, the better.. Me personally, I would go with a 10 gauge stranded wire... or even 8 gauge... if you can... That'll protect you for up to 50 and 75 amps..
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Re: Battery cutoff switch and msd, car wont die
[Re: challengermike]
#1478090
08/03/13 10:28 AM
08/03/13 10:28 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
Quote:
Quote:
I put a diode in my field wire,that fixed mine 
Good idea 
I may try this today. I have 1 that came with the msd box. Not sure if it will work ok with the resister but I will give it a try. I like the idea there is no power in the car with the disconnect switch off.If this doesn't work I may try running the msd off a relay.
On the 4 post master.. I dont know how many amps it
can handle but if you ran the field wire to the small
post it will do the same(any way to turn off the alt..
but if you isolate the large alt hot lead I have never
seen a issue (using isolated clamps to hold it on
the frame)... I prefer to do it the easiest way possible
because if it brakes down at the track you want to
be able to fix it easy.. thats why I dont run a diode
or a solenoid to kill it... the old KISS system..
if you wanted you could run a 100 amp fuse at each
end of the alt lead(1 at each end would cover a short
anywhere on that line).... JMO
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Re: Battery cutoff switch and msd, car wont die
[Re: challengermike]
#1478093
08/03/13 12:32 PM
08/03/13 12:32 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
The diode idea didnt work I just tried it. And a solenoid wont either do to it needing a power loss to kick it off and nothing losses power with the alt powering it. I guess I will just run the alt wire and msd directly to the bat itself. I do like the idea of fuses on both sides of the alt line. And for what it's worth I tried the msd on the back of the alt and with the new box it didn't die either. Maybe because it's digital and not analog like the old box. I don't know why with the old box it would kill the car.
Is your alt a single wire(hot only) or is it using
a external regulator.. if it has a external regulator
you have 2 field wires... one is a sense wire and
the other is keyed hot.. if you break the keyed hot
lead you then kill the alt... here is a simple wiring
diagram of how the system works
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Re: Battery cutoff switch and msd, car wont die
[Re: MR_P_BODY]
#1478094
08/03/13 12:49 PM
08/03/13 12:49 PM
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Joined: Aug 2003
Posts: 1,062
Amherst,NY
challengermike
OP
super stock
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OP
super stock
Joined: Aug 2003
Posts: 1,062
Amherst,NY
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My alt is wired this way
S - connect this right to the "+" on the Alt. with a ring terminal
F - Not needed
L - Connect to 12V source with a 3-4 Watt bulb in the circuit (see web page on CS130 repair) I have a resister instead of the bulb
P - Not used
And the big Wire go's to my starter and back to the disconnected side of my cutoff switch.
Also on the stud the alt is 1 wire that go's to the starter, 1 wire that jump's the s terminal to the stud, and I have my cooling fans wired to it.
The alt is internally regulated GM CS130
I have no stock wiring in the car, The person I bought the car from wired it himself. The whole car is wired off the disconnect side of the cutoff switch.
Last edited by challengermike; 08/03/13 01:14 PM.
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