battery cut out switch

[H. L. Chauvin]

FWIW: Bought a heavy duty Marine Cylindrical Disconnect Switch about the same size as the heavy duty vendors' lever type cylindrical disconnect switch offered; except, for a slight bit of additional theft protection, it has a keyed switch with a removable key.

It is mounted with (2) thru-bolts through a piece of wood neatly fitted in the oblong steel cross member's opening immediately behind the battery, with a thin metal plate above & accessed through a round hole cut through the plywood floor board under the floor carpet.

No holes were drilled through body sheet metal & no holes were drilled through the Model A's steel chassis' frame.

For a bit of additional theft protection, the top of the key, when inserted in the switch, is flush with the top of the plywood floor board, so the carpet above when laying flat, conceals both the inserted and/or non-inserted key & the disconnect switch. Also, sliding feet on the floor board upon entering or exiting the vehicle never hit a protruding part of the concealed switch or key.

The switch, like that always recommended for Marine Safety applications, interrupts the battery's ground cable.

It was only used often when totally rewiring the entire vehicle with all new wiring, & it is intended to be used only when the vehicle is not in a locked, secure garage and/or left parked unattended like at a restaurant and/or parked unattended overnight at a motel.

Hope this helps.

 

[Hoogah]

I used a pre-existing hole in the firewall that a previous owner had used to install a foot-operated dip switch (go figure!). The part of the switch that protrudes into the cabin is black plastic, but you can't really tell unless you get right down there! It has removable key which means I don't really have to conceal the switch for security purposes. The switch cost about $30. Re-routing the cable to this position was not difficult and didn't use excessive length of cable. The key looks like it's too close to the starter switch, but that changes when it's in the ON position (rotated 90 degrees clockwise). This is a RHD '28 phaeton.
Pardon my paint (or lack thereof!!)

 

[Tom in SW VA]

Mine in mounted on the motor mount on the driver's side. It was installed when I purchased the car. It is a toggle switch.

 

[MikeK]

What concerns me about those battery post open knife switches is the size of the post they are made to fit. The Positive and Negative posts are different sizes, so those devices only fit one of the two correctly. WHICH ONE? I would never put a cutoff switch on the "hot", only the ground lead.

 

[Super88]

I agree tiger.1000 and this is not what I plan on using, but was just offering the info for those that might be interested in this type. I haven't looked closely yet, but I will place my switch where it can easily be reached from the driver's seat for speed and ease of use.

 

[ThosD]

Resurrecting this thread. I recently purchased a cut out package as described above that provides a mounting bracket that attaches to the starter. All current from the battery is routed from the negative terminal and through the fuse on the starter. It seems that breaking the current path at this location removes the battery from all electrical components of the car. How is this less safe than breaking the circuit at the ground strap that connects the positive post to the chassis? However, I would prefer to mount the cut out switch inside the cab and breaking the ground strap would be more convenient.

 

[bbrocksr]

Do the ground cable and mount it by the drivers seat. If you put it in the hot cable everything before the switch is still hot.
Bill

 

[ThosD]

Bbrocksr
Thanks you for the reply. I may be over thinking and confusing myself.

Respectfully, I still have questions. If the negative post is not connected to anything, no current will flow through the battery; yes? Connecting the chassis to an earth ground (touching the car while standing in a puddle of water) while there is a break in the hot cable will not cause a current flow through the battery; yes or no? Ford fused the hot side, not the ground side. Why not switch the same side of the circuit that Ford fused?

 

[ThosD]

I got this reply from another forum:

Standards over the years migrated to never disconnecting “ground” for safety & consistency, and not just in car batteries.


Some reasons:
The idea/message of disconnecting power source at the “0V” side is counter-intuitive, and in some cases dangerous.
ex: is disconnect connector fully insulated (since some parts are always live)? 0V connections are seldom insulated, while power i.e. 12V or 6V usually are.
Newer systems cover the “hot” terminals.


Ground leads are often physically harder to connect to in some cases- i.e. braid, straps, metal rods or in a tight space, vs. insulated wire coming off the “hot” side, to a switch that can be located elsewhere (with insulated connector cover)


Not saying a model A has any of those situations.


Motorhomes using multiple +12V batteries for vehicle starting, house or other aux battery banks always disconnect +, usually with a big knife switch. Some are more sophisticated and have shared power mgmt between all.

 

[bbrocksr]

What happens if you strike you wrench while disconnecting the hot cable?
What happens if you strike your wrench while disconnecting the ground cable?
With the ground disconnected nothing is hot. If you put the switch in the hot cable everything before the switch is hot.
Bill

 

[Brentwood Bob]

Good to avoid sparks.

 

[Bruce of MN]

I don’t believe that Ford had any fuses in the Model A.

Bbrocksr
Thanks you for the reply. I may be over thinking and confusing myself.

Respectfully, I still have questions. If the negative post is not connected to anything, no current will flow through the battery; yes? Connecting the chassis to an earth ground (touching the car while standing in a puddle of water) while there is a break in the hot cable will not cause a current flow through the battery; yes or no? Ford fused the hot side, not the ground side. Why not switch the same side of the circuit that Ford fused?

 

[ThosD]

Disconnecting a battery is a different concern. If the cable from the negative post of the battery to the fuse is disconnected, every thing on the car is at the same potential as ground. If the live end of the hot cable is contained inside of a switch body, no contact will accidentally be made. Sparks only occur when completing a path that connects the negative and positive battery posts.
To the best of my understanding, placing the cut out switch on either battery cable will create a desired and safe arrangement if the cable is well insulated. Just be careful when disconnecting the battery.
For my installation, I will be using insulated cables on the ground terminal because I want to access the cutout switch from inside the cab, on the seat riser.

Thanks for chatting, folks.

 

[bob from red oak]

when i bought my A it had one mounted on fire wall on the left side of the steering column. It has worked fine as I open the door and turn the switch before I get in the car and turn it off after I get out. Not that inconvenient.

 

[ThosD]

I don’t believe that Ford had any fuses in the Model A.

Thanks for the clarification. The aftermarket fuse on top of the starter looks like a factory item on my car. It appears that this was an early common mod for the A.

People create sparks when working around the unprotected hot terminal that is on the starter. Wrench or screw driver touches the hot terminal and the engine block or control rod or any other part of the car and a spark is created; like a spark plug. When working on or around the electrical parts of the car, the battery should be disconnected at the ground first. Because all body parts are also at ground voltage, no sparking occurs when a tool bridges the the ground terminal of the battery and other grounded items.
Since it's a pain in the neck to access the battery ground strap, a cut out switch mounted on the ground cable provides an easy to reach switch for safely working on the A as well as saving the battery when parked.
Tom

 

[SeaSlugs]

Mikes sells a kit with a switch bracket that fits on the starter bottom bolt. HERE

i may have to go this route - really dont want to make holes in a very very nice 28-m30 cab i have and theres no real good way to mount it without getting in the way of the already cramped foot space with the AA dual high down there too.