Master disconnect question

[cbodybob]

Ok went out to remove my alt. thinking I may have a bad one. Disconnect switch off. When I removed the wire from the disconnect switch from the alternator lug I got a lot of sparks. Put my tester on the wire end & reading 12 volts. So my battery has been on a slow discharge in the staging lanes last 2 races. Figured I would test alternator. So how can I have voltage at the terminal from the switch? With the switch off. Could it be bad & causing my discharge?

 

[Dako]

Did you disconnect the battery 1st? That lead is circuited to the battery. It is used to provide the output generated by the alternator to the battery. Always disconnect the battery 1st when working on the charging or starting system...unless you like welding using battery power.

 

[67 coronet]

i always use a bat disconnect at neg bat cable.no problems with that.your switch may be bad.

 

[cbodybob]

No I thought switching the master off would do that. I have been teched fully once this year & the switched it off while car was running.

 

[khryslerkid]

You're talking about a emergency shut off on the rear if your car.

I would think that would be wired to kill the whole system, not just the ignition and start. I never read the rules on that but if it was my car it would be wired to totally disconnect the battery supply from the car. What does the tech rule say about this?

You're definitely not wired to totally isolate the battery supply from the system. If your main alternator wire is being ran through your kill switch and you have 12 volts when switched off, sounds like a bad kill switch. Disconnect one side of the kill switch and see if that kills it at your alternator.

Or test voltage at both terminals on the back if the kill switch in each position, on and off.

 

[Budnicks]

How did you wire the system ??
is probably the next question that should be asked,

do you have a schematic or diagram you can share on how you wired it ??,
maybe it just wired wrong,

all mine would kill "all power", form "after the switch",
like fuel pump, water pump, electric fans, ignition, charging, lights etc.,
at-least on all the cars I've done...

IIRC that's how NHRA wants it wired too... to kill everything not just ignition
You may want to recheck the wiring & the tech rule book too...

 

[cbodybob]

Yep mine kills all power. Or at least it used to. The tech guy had me start it up & he switched the master off & the car shut down. This was early this year at a TnT. Has been wired like this for maybe a year. I dont have a schematic. I can tell you I bought it from Jegs. They called it a kit to kill the alternator. No instructions. Its a 8 ga red wire. So I ran it from the pos side of the master cut off mounted at the rear bumper all the way up to the large alternator lug. I always switch the master off when the car is not running or in the stanging lanes. After I installed I had some other racers suggest I run it to the main starter lug. Told me thats how their car was. But if its hot all the time ..... I just dont believe it has been like that. I'm certain I checked that when I installed it. Another thing by wiring it this way it really help my charging. It would read over 13 volts while going down the track. before it would only get to 12.4 or so.

 

[Budnicks]

not sure what to tell you... sounds like something is bypassed, or you wouldn't have any power at the alternator when the switch is off/pulled

I would think if the switch was bad...
You'd get no current anywhere, unless it failed by keeping the circuit closed maybe...
not really sure....
here's a few

yours is "maybe/probably" ?? wired like the 3rd one down A & B with the alternator hot,
that says choose A or B but not both...


I Google searched, to see different types, there are a ton of them, way more than I ever knew...
NHRA Battery Safety Cutoff Switch wire diagram schematic

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that's the best I can do for you

 

[cbodybob]

Man I dont think mine is like any of those. I will work on it some tomorrow. I think something is wrong. I dont have power anywhere else when the switch is off, so why would I have it on the lead going to the alternator? Switch off and car not running obviously.

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Budnicks thanks! That took a lot of effort. I'll get back on it tomorrow.

 

[bm02tj]

The kill switch has to separate the alt from the run side
If you just disconnect battery it will run on the alt
So to do it right it needs to be a 2 or 3 pole switch

 

[cbodybob]

Its the 250 amp 2 pole switch Jegs sells. Before I ran this wire to the alt the kill switch would not shut the car off. Now it does.

 

[cbodybob]

Ok mine is wired kinda simple. It's simply is after the battery. It's a 2 post moroso. When I added the alt wire I should have got a 4 pole switch. So that's why I have power at the alt lead with switch off. So my next question? Can I run the wire to the starter lug instead of the alt lug to keep from having to buy a 4 pole switch?

 

[bm02tj]

No you have to switch the alt wire or car will keep running

 

[cbodybob]

Ok, thanks. I just ordered a 4 post Taylor switch from Jegs.