Battery cutoff switch
- Thread starter 30-9
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Lanny
Well-known member
Flaming river has a good quality disconnect and cole hersee also has a suitable master disconnect switch , I always connect to the ground side ,if the ground is disconnected you can short against the positive terminal to the chasis and be safe from shorting out, if the positive is disrupted the positive battery terminal can be shorted to ground and cause problems.
39portlander
Well-known member
Battery cut-off on my 39 and 77 got them from the Autozone, made in the U.S.A. Mine are on my positive as they are 12V, yes put it on your negative.
If you recall in most service books they ask you to "dis-connect" the negative side of the battery" before doing a repair. Same idea for your application with 6V.
This thread can quickly turn into a thread about "what is the best Oil" good luck
Scott
If you recall in most service books they ask you to "dis-connect" the negative side of the battery" before doing a repair. Same idea for your application with 6V.
This thread can quickly turn into a thread about "what is the best Oil" good luck
Scott
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V8 Bob
Well-known member
You will find most professionals switch the "hot" lead, including the NHRA, and that would be the negative side of the battery on a positive ground system.
One of the best is from Pollak, like below, and is what I use on all my cars. Avoid the cheap "green" switches that clamp to the battery post, especially on a 6 volt system.
Note-I had to delete the original earlier post because of a picture problem.
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Steve/IL
Senior Member
Be careful when you buy a disconnect switch. There are 20 amp continuous duty switches which I do NOT recommend. Look for at least a 175 amp continuous duty switch. Prices are all over the map. A good 175 amp switch should be in the $40 range, but there are switches for 2 and 3 times that amount.
SofaKing
Well-known member
Put it on the ground side, you are trying to isolate the battery from discharging when not in use. If you put it on the "hot" side, when you lean over the fender to operate it, you are the new path to ground.
I always understood the NHRA switch to be there at the back of the car so that ground crew can shut off all power in case of a fire so it was safety issue.
I always understood the NHRA switch to be there at the back of the car so that ground crew can shut off all power in case of a fire so it was safety issue.
supereal
Well-known member
We have used the "cheap green knob" switches for years with no problems. They go on the "hot" side of the battery, not the ground. They are a good way to prevent battery discharge when stored if you forget to pull the clock fuse, etc. Also good for fire prevention with all the old wiring in the vehicle. If somebody wanted to steal your car, a switch might slow them down, but is unlikely to prevent the theft. The green knob can be unscrewed a removed , if preferred, if theft is suspected.
Been using the the Cole Hersee switch. Best quality, believe they are still made in the USA at Cole Hersee in South Boston. Some favor switching the positive or hot side. NHRA or not, the best method is switching the ground. With the ground disconnected nothing happens anywhere, now how.
1938 Coupe
Senior Member
Green knob cut off should only go on the negative post of the battery. If you noticed it only fits the negative post. The positive battery post is larger and the only way you can make the green knob cut off switch work on that thermal is to spread it open. That's why there are two different sized thermals so you know the difference! Go figure!
JSeery
Member Emeritus
I have no idea why you would want to put the switch on the ground side. The "hot" side is where the switching goes.
"With the ground disconnected nothing happens anywhere, now how"
How would anything happen with the "hot" side disconnected? The ground comment makes no sense.
The cable from the hot post to the switch will always be hot whether the switch is on or off.
If the switch is installed in the ground nothing is hot when the switch is off,
Bill
Drbrown
Well-known member
My '47 has it's Green Knob on the 12v neg ground side and this ground is connected directly to one of the mounting bolts on the starter. The engine has two ground straps; one to cowl near dash board; one to frame. I added #8 ground wires from engine to (1) rear of car near lights, and (2) vicinity of head/fog/parking lights.
Our "modern" 12v family cars have neg ground systems. Their manufacturers say disconnect ground when working on car to avoid damage to non-ignition activated uses (radios, clocks, door locks, security systems, monitors, etc).
Our "modern" 12v family cars have neg ground systems. Their manufacturers say disconnect ground when working on car to avoid damage to non-ignition activated uses (radios, clocks, door locks, security systems, monitors, etc).