Battery cutoff switch at the starter?

roccaas

roccaas

Well-known member
After reading Jay Leno's horror stories about a Cord that burned down when the dome light stayed on, I'd like to put in a cutoff.

Rather than pulling up the carpet and removing the battery hatch, is there a quality way to put the cutoff at the battery cable to starter lug connection?
 
Yep, just under the front of the seat so you can get at it easily at any time. This makes the cables a tad longer so I would recommend larger #0 cable. I like heavy wire, I still wire a house with #12 as I don't care for #14 [ its sure easier to work with though].
 
I have installed several using a Model-T short starter cable and a battery cut-off switch that vendors like Snyders sell. The cut-off is mounted in the left rear motor mount block with the switch facing upward through the hole. When the zinc switch knob is painted black, it makes it very obscure to the casual observer, and the Model-T cable is also a cloth wrapped wire so it all looks very period to all but an astute observer. The original-style Model-A starter cable is removed from the starter switch and now attached to the cut-off switch lug, ...and the Model-T cable is attached from the other cut-off switch lug and now carries the connection on to the starter switch terminal post.
 
I used a top quality Cat shut-off switch that uses the Cat key to activate.Itworked fine for a year then developed an open circuit when in the 'On" position.I,ve eliminated the cut-off & use a 30 amp breaker mounted on the inner 2 starter switch screws.I only had to slot one of the mount holes on breaker to use both screws.I also have 20 amp modern type fuse holders for lights & horn.
 
You can get a bracket from the vendors that will mount it by the starter. The bracket is mounted to one of the starter bolts. Yes you do need to lift the hood each time, but a Model A being what it is, it is good to look at the engine compartment prior to taking off on a run.
 
I have the heavy duty brass switch going through my firewall above the starter button shaft so I can easily flip the switch on or off with my toe any time I park for a while.
 
I have 2 A's with cut off switches, both mounted under the seat and switching ground. Your preference on what to switch. I went with the better heavy duty switch, don't like plastic and heavy amp draws
 
Likewise under the seat.
There are some el cheapo switches out there - expect to get what you pay for and look for a decent one and fit it somewhere that is easy to get to - that way you are sure to use it every time you turn the car off.

It is good to know that everything is isolated with 1 switch.
 
I mount mine on the ground connection (in the case of the model A, the positive pole)

The reasoning is this :

1. For the model A this puts the switch in the perfect place, just in front of the seat riser, where you can quickly get at it. At the same time, it should not interfere with the pedals and your feet.

2. It is safer to isolate the chassis from its battery pole than to isolate the live harness from its battery pole - because the chassis is everywhere, whereas the live harness is only along the wires. Or said in another way - when you turn off the isolator switch (mounted on the ground, chassis, positive terminal), the only realistic possibility of a short is to drop something which by coincidence has to hit both battery poles simultaneously. If you have the isolator switch on the wiring side, it is enough to drop something that contacts the wiring (negative) pole, and just about anything else close (the chassis) to whatever you are dropping will be firmly connected to the other pole. Hence, the probability of still having a short will be significantly higher with the switch on the wiring (negative) side of the battery.
 
BillLee/Chandler said:
Agree completely that the switch should be in the ground cable. My installation is (poorly) written up at my club's website: http://www.cedarcreekas.org/TechTopics/CutOffSwitch.pdf
Click to expand...


OK, I know y'all have said this before but I honestly do not understand why you guys say that it needs to be on the Ground cable. While I am not here to argue, the following sanctioning body rulebook; NHRA, NASCAR, DIRT, all specify that the disconnect must be on the Positive cable. What is it that you are seeing that these large racing organizations are missing?


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Brent,

I'm not saying that the switch NEEDS to be on the ground cable, only that it in my view, for the reasons stated in my post, is BETTER if it is on the ground cable.

Mounting the isolator switch on the live cable is still miles safer than no switch at all.

By the way, you state that "NHRA, NASCAR, DIRT, all specify that the disconnect must be on the Positive cable." Now, what does positive cable mean on the model A ? :D:D

QUOTE=BRENT in 10-uh-C;681589]OK, I know y'all have said this before but I honestly do not understand why you guys say that it needs to be on the Ground cable. While I am not here to argue, the following sanctioning body rulebook; NHRA, NASCAR, DIRT, all specify that the disconnect must be on the Positive cable. What is it that you are seeing that these large racing organizations are missing?


.[/QUOTE]
 
BRENT in 10-uh-C said:
OK, I know y'all have said this before but I honestly do not understand why you guys say that it needs to be on the Ground cable. While I am not here to argue, the following sanctioning body rulebook; NHRA, NASCAR, DIRT, all specify that the disconnect must be on the Positive cable. What is it that you are seeing that these large racing organizations are missing?
.
Click to expand...

A couple of points:

1) Most of us are not racing our Model A's in NASCAR, NHRA or DIRT competition. :D

2) Positive or negative ground?

3)As was pointed out in an earlier post, having the switch in the ground cable protects the ENTIRE system, where in the "hot" cable does not. I.e., any short from the hot post (on the battery or anywhere in the wire up to the input post on the switch) to the frame or any other adjacent area will still be a dead short and will ... well... burn the crap out of stuff! :)

(That's a technical term: "Burn the crap out of stuff!" :p )

Note that I do NOT say "positive" or "negative" since many A's are positive ground, and many are negative.

Adding ANY sort of cut-off switch increases the safety in an A. Unfortunately I see many added AFTER the cable from the battery to the starter. And all you need to convince yourself that that is the WRONG place is to have a starter switch stick one time. OTOH, the switch in the ground cable will protect even the starter with the stuck switch.
 
I once saw a guy in the National Guard disconnecting a battery on a 24 volt system. He was starting with the "hot" terminal. Wrench on the battery terminal hits a piece of the body on the first twist and really did a job. Ruined wrench, nice notch in the sheet metal, good chance for burn or fire. Having a disconnect on the GROUND side eliminates all of those possibilities. Single disconnect on the ground side is all that is needed for old street driven Fords. The racing organizations also require a simultaneous shut off of the alternator. If an engine is running and the battery is disconnected, the alternator or generator will still supply enough juice to keep the ignition hot. So if a drag racer crashes, the (externally accessible) switch will both disconnect the battery AND the alternator killing the ignition.
 
I like them in the ground side because of the problems I've seen with my own two eyes,not third hand stories.Two of them were on A's.On one the guy mounted the switch up on the firewall,it was pretty slick.He could flick it with his toe and then start the car.Then one day the cable pulled out of the lug on the back of the switch.We don't know if the cable was poorly crimped,corroded,or if a pedal caught it,but the end result was the same.That hot cable dropped,and it must have bounced around some,there were weld marks on both the starter and the steering box.Luckily the battery exploded right off so the current was lost.The most damage was to the paint.The explosion managed to nail the backs of all four wheels with acid.Another I saw was another one mounted to the firewall.The owner was tinkering and decided to reposition the terminals on the battery.He felt they were too close to the hold down.When he pulled the hot cable to stretch it he pulled it taut against a lip on the firewall,or maybe a floorboard screw.A few weeks later his wife started hollering about smoke and a rotten egg smell,he pulled over and kicked the switch off but it didn't do him any good.The cable was grounded between the battery and the switch.All he could do was to watch it smolder until something burned enough to break the connection.
 
In addition to what Keith just said, I've also seen the cheap plastic cutoff switches melt and drop the hot cable. I'd also use the ground side and a quality switch, if I was going to install one.
 
Guys I am confused (which is normal for me). In the std Model A setup, the "positive" (+) battery terminal goes to a "ground". Thus is this the "ground" cable? This may be a self answered question but I get confused when we talk about "ground" which I normally think of the "negative" battery terminal as the "ground". Anyway I guess I may have answered my own question.
 
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