Master Disconnect Ground Circuit Route?

[leo]

OK, I'm challenged when it comes to understanding circuits. The last time I visited this topic the concensus was to break the ground wire with the switch. So to me this means that the negative battery post gets connected to the starter as normal and the positive battery post goes to one post of the master switch and the other post of the master switch goes to the ground. To do this we can no longer use the ground strap cable because it is too short. What cables do I need to buy and where should they be routed and connected?

[Tom Wesenberg]

I don't see the need for a switch and don't use one, but if you want to install one I'd probably stick it in the top hole of the left rear motor mount. Brent had posted a picture of one mounted there. Measure the cable length and go from there.

[denis4x4]

Master switches are great as an anti-theft device and provide an extra measure of safety over the winter when using a battery tender. Too, I recommend a metal one with a metal key like the ones sold at So-Cal Speed Shop. I've replaced all of the cheapo chinese switches with the So-Cal units.

[Jack '29 Sport Coupe]

Most of the auto parts houses sell them in different lengths. Use a "0" or "1"
gage. JMHO

Jack

[Rainmaker Ron]

Originally Posted by leo

OK, I'm challenged when it comes to understanding circuits. The last time I visited this topic the concensus was to break the ground wire with the switch. So to me this means that the negative battery post gets connected to the starter as normal and the positive battery post goes to one post of the master switch and the other post of the master switch goes to the ground. To do this we can no longer use the ground strap cable because it is too short. What cables do I need to buy and where should they be routed and connected?

I believe you will find a spot about 6 inches left of center and immediately in front of the seat riser. The cable from the battery post to the disconnect switch must be insulated. The 19 inch cable available for use to the starter works just right. Your old ground strap can be reused from the switch to ground. This installation requires some effort but in the end is neat, reddily accessable and uses the shortest cables. If you plan to just stick it in the first hole you see and string cable around like spaghetti, I would save the money and reduce the probability of shorts and fires. If an emergency disconnect is not accessable in an emergency, whats the point? I second the motion also to use only a quality switch.
Rainmaker Ron

[bobpo]

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I use the metal disconnect switch and have it mounted just below my left knee on the seat riser in my '30 coupe.

I find it to be Very Useful for a couple of reasons. First and foremost is that I have a tendency to bump the headlight switch and if I don't turn the power off I would have a dead battery. I'm new to this Model A thing and eventually maybe I wouldn't need it. (maybe) Secondly would be the theft factor in that it is hidden from view unless you squat down and look in floorboard level.

It's very convenient to turn/off as you get in and out of the car.

I'm very happy I installed it. Cost about $24.00 plus additional cables. Easy installation too. Biggest problem was drilling the hole in the front of the seat riser which I did with a step drill bit.

Good Luck

[leo]

Hey guys, thanks for the input, but I really did not phrase my question well so I will try again. I do have the metal housed switch which Bratton sells and I want to mount it in the drivers side motor mount because I do not want to drill any additional holes. That being said, what size/length cables are needed to connect to the switch from the positive battery terminal and then from the switch to some grounding point on the frame? What is the best route for these cables so they do not get touched by the action of the clutch and brake pedals?

[Kurt in NJ]

When looking for cables take a magnet with you, the terminals on some of the pre-made cables are steel --a bad connection soon to happen

[CarlG]

Originally Posted by Rainmaker Ron

... Your old ground strap can be reused from the switch to ground...

I don't know just how that would work, since the cable ends would not be the same coming off the switch as it would have been coming off the battery.

[leo]

I may have to cobble something together from one or more cables.....someone must hve done this before.....

[1931 flamingo]

I believe snyder's offers cables and a little note on how to and which ones needed.
Mine is mounted under the driver's seat, convenient and out of sight.

Paul in CT

[leo]

Yes, the dealers do sell a cable to be used with the switch, but the cable is for the switch being wired to the starter, not the ground which is the way everyone says not to connect it.....

[Rainmaker Ron]

Originally Posted by CarlG

I don't know just how that would work, since the cable ends would not be the same coming off the switch as it would have been coming off the battery.

Good catch Carl, the length is ok but the end is wrong! In practice I have a stock of cable and ends and make them up as needed. The hook-up I described would require the purchase of a 6 inch cable with an eye on each end. Looks like you were the only one to read and understand my post.
Rainmaker Ron

[Rainmaker Ron]

Originally Posted by leo

Yes, the dealers do sell a cable to be used with the switch, but the cable is for the switch being wired to the starter, not the ground which is the way everyone says not to connect it.....

Not everyone! In fact, going to the extra effort to break the "hot" side creates more places for shorts to occur and the "juice" cares little where it is interrupted.
Rainmaker Ron

[Louis]

LEO,
This is how I mounted mine, it's a cheap plastic one from harbor frt.
I did buy a 19" cable from auto zone [a 17" would do. i ran the old cable that was on the starter to the new cut off sw. and ran the new 19" cable from the new cut off sw. to the starter. i did have to reroute the new 19" cable some, you will see when you get under your car.... Im circuit challenged also.
If i can help let me know, my email is [email protected]

To be safe i would disc. your batt. before you start.

[Keith True]

To break the ground side,and install the switch where you want it,you are going to have to mount the switch and measure what you need for cables.I've never mounted one that way,so I wouldn't have a clue how long to make the cables.I've mounted them in the floor and in the seat risers,I measure what I need for cables and whack it off the roll.You can buy cable by the foot at GOOD parts stores,(not Auto Zone,Pep Boys,etc)and the crimp on ends.I would probably run the cable up the drivers side frame rail,then from the switch to a starter bolt.Myself,if I am going to use a switch,I want it where I can get at it.I've put a few in,but none of my own A's have one.Most of my equipment has them,loader,dozers,excavator,backhoe,tree chipper,I guess everything except my old Bobcat.On all the equipment the switches are all out where I can walk up to the machine and hit it.I don't want anything that I have to open a cover to get at.

[Bill Goddard]

What is the electrical reason for putting the switch on the ground side or the battery to starter side? If you interrupt the ground side can you still short out a tool against the frame (ground) in the engine compartment? And if you interrupt the starter side can you still short out against the frame? Bill G

[Mike V. Florida]

Originally Posted by Bill Goddard

What is the electrical reason for putting the switch on the ground side or the battery to starter side? If you interrupt the ground side can you still short out a tool against the frame (ground) in the engine compartment? And if you interrupt the starter side can you still short out against the frame? Bill G

If the battery is disconnected from the frame there is no path back to the battery, so no short.

When installing a switch just be sure that correct size cables are used. !2 volt cheap cables are too small.