questions about battery disconnect wiring

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Mine is probably a little complicated but it works and the car dies with the disconnect and no power goes past the switch after that.

Battery To 4 pole disconnect
Disconnect has two wires off of the large lug,
One wire goes to the front of the car for power distribution
One wire goes to a ford style solenoid in the trunk, that has a lead to the starter
I use a solenoid off of a Jeep that works with the stock style neutral safety switch(requires ground to start).

Up front the alternator feed goes to a Cole hersey solenoid then into my power distribution. I have the solenoid operated off of keyed ignition that runs through the small poles on my disconnect switch. When you kill the disconnect it kills the solenoid and in turn kills the car.

I only use the stock wiring for the lights and wipers, everything engine related is run off of the Megasquirt controller.

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What this is doing

Start at top left the blue "cut" wire. That is the original "ignition run" wire coming out of the firewall/ bulkhead connector from the ignition switch, and out into the engine bay. It originally fed several things "under the hood" depending on the car model, year, and accessories.

At the very least in 72, it feeds the igntion system, the blue alternator field, and the power to the voltage regulator. It may also feed the electric choke and some smog control doo-dad

That original circuit is subject to voltage drop problems which is why the idea of a relay or continuous duty solenoid. The key turns on the solenoid, and the solenoid then feeds the loads thus relieving the wiring.

NOW Notice that in this modification, the "cut blue" coming out of the bulkhead is wire to the rear, to one terminal (small) on the disconnect, and BACK up front to feed the solenoid. The key switch is turning on the solenoid through the disconnect, and allowing the thing to operate. So when you pull the disconnect, this drops out the solenoid and kills BOTH ignition power, and the voltage regulator and field power. It can not run on

ALSO NOTE that you can easily create a sort of anti-theft by hiding an extra toggle switch in the solenoid circuit, OR IF YOU MOUNT the disconnect inside the trunk, and operate it with a push-rod, you can easily create a rod-inside-a sleave set up where the switch can be "pushed" off, but cannot be turned back on with the pushrod. You have to unlock the trunk to re-power the disconnect.

Del, Is this what you are saying? Use the original 'run' feed to control a relay, and power the ignition etc through the relay?
upload_2020-2-10_8-29-4.png


The alternator output could also go direct to the relay.
 
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That will work. There was a diagram of this floating around these parts. The only real difference between Crackedback and the above, is his method requires a separate "fairly large" (no6 or larger) to go up front along with the big main cable. His method keeps the big cable cold except for starting. If the no6 wire is properly protected, this reduces further the danger of high current shorts.
 
Thanks.
Crackedback's is pretty nice setup too.

The alternator output could also go direct to the relay.
Figured better show it is understood that the connection is into the main circuit.
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That will work. There was a diagram of this floating around these parts. The only real difference between Crackedback and the above, is his method requires a separate "fairly large" (no6 or larger) to go up front along with the big main cable. His method keeps the big cable cold except for starting. If the no6 wire is properly protected, this reduces further the danger of high current shorts.

I like that the ford solenoid means the starter cable is disconnected most of the time. But on second reading, I'm not clear if the alternator is protected the way you prefer.
The way I understand crackedback's panel, the alternator output goes all the way back to the continuous duty relay. So if either the disconnect or the key switch is opened, the relay interupts the output at the same time as ignition is killed. Is that quick enough to prevent flyback voltage?
 
@67Dart273
I was directed to this thread by @Mattax. I’m going to start gathering parts for an NHRA legal trunk battery install. It’s a 74 Dart Sport with stock wiring, alt., etc. I know this is better than NHRA’s method, as there is no hot wire running to the front when the CO is thrown.
I’m not an electrician. But I can duplicate this.
Two questions (so far)-
-The 4 ga fused wire. A fusible link? An inline? What rating? I think a 4 ga fusible link has a specific rating?
-The CDR, will a cole hersee 24059 or 24106 work as @crackedback suggested?
 
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I would get the 24059 (4 terminal) simply because the extra coil terminal gives you "other options." For one, an easy path to a simple anti theft. You can run a small wire, no 18, or what, to a simple unobtrusive switch, to "kill the whole deal" when out of the car.
 
Something I didn't see mentioned, but you do not want the battery box "sealed". It needs to be vented.
 
Crackedback's wiring method has the advantage of leaving the big feed to the starter dead except for starting.
67Dart's approach has the advantage of a shorter path for alternator power.
You could combine them.

The way I drew it above, only a 16 ga fusible link is needed. That protects the 12 ga wires. If the feed to the starter grounds, or even the one up to the starter relay, the battery will discharge through them until the connection is broken.

If something needs a 4 ga wire, then maybe it can be protected with a maxi fuse.
More likely what you can reasonably protect is the smaller wires after the 4 ga wire.
You may want to do both.
 
Crackedback's wiring method has the advantage of leaving the big feed to the starter dead except for starting.
67Dart's approach has the advantage of a shorter path for alternator power.
You could combine them.

The way I drew it above, only a 16 ga fusible link is needed. That protects the 12 ga wires. If the feed to the starter grounds, or even the one up to the starter relay, the battery will discharge through them until the connection is broken.

If something needs a 4 ga wire, then maybe it can be protected with a maxi fuse.
More likely what you can reasonably protect is the smaller wires after the 4 ga wire.
You may want to do both.
I see what you mean about the wire to the starter being hot all the time. I don’t want that. Darn, I thought I had it. lol I’ll have to study your diagram and get back. Yours is a combo of 273’s and crackedback’s? I’m sure I’ll have questions. I did my Mustang per the NHRA rule book, and I have to update that too.
 
Let me try to clarify what I meant.
Illustrated below applies a relay as 273 suggested to a car where an in-line ammeter is being used.
Much of the wiring is same as factory. Alternator output wire is factory (black either 12 or 10 ga).
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Below is way to do the same thing, but with a solenoid in the starter cable.
The 8 gage battery feed is protected by the 12 ga fusible link.
upload_2022-3-27_12-58-48.png


In both the relay is only carrying current to the ignition and alternator's rotor.
That could be as low as 3 amps or as maybe as much as 7 or 8 amps with a later model alternator and/or an ignition like MSD's that can draw 1 amp per 1000 rpm. (That's from MSD's instruction booklet, I've not tested it).
The point is that max through a relay used this way is much much less than the maximum current of a relay in the alternator's output wire.
 
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Thanks for all your effort. I’ll get the stuff I don’t have and start on this. (No pun intended). I’ll be back with more questions, I’m sure.
 
Already questions…
What gauge should I use between the Ford sol and the car’s starter relay, and between the cut off and the CDR?
I have 6 ga I’ll use instead of the 8, just because I have it.
 
I think I have everything except the cut off. What rating do I need? I accidentally ordered a 2 post Moroso. 175 amp continuous, 1000 amp surge. That has to go back.
I see a Moroso 4 post 74108 https://www.amazon.com/dp/B01GWD2XUS/?tag=fabo03-20 I can’t find specs on it, but all four posts are 3/8.
And a Taylor 1033. 100 amp continuous, no surge rating.
Taylor Cable 1033 Taylor 4-Post Battery Disconnect Switches | Summit Racing Rather cheap. Too cheap?
I must be missing something in searching these.
 
Here's how I made it work. 2 fields on the alternator. 1 is keyed live. Disconnect that wire. Now run a wire to the master on off switch so that wire turns off with the switch. Only drawback. This wiring is always live and will sap your battery. Turn the switch off when parked.
 
I think I have everything except the cut off. What rating do I need? I accidentally ordered a 2 post Moroso. 175 amp continuous, 1000 amp surge. That has to go back.

I see a Moroso 4 post 74108 https://www.amazon.com/dp/B01GWD2XUS/?tag=fabo03-20 I can’t find specs on it, but all four posts are 3/8.
And a Taylor 1033. 100 amp continuous, no surge rating.
Taylor Cable 1033 Taylor 4-Post Battery Disconnect Switches | Summit Racing Rather cheap. Too cheap?
I must be missing something in searching these.
I just ordered this:
Cole Hersee 75907-BX Switch (Rot 2 Position Lever) | eBay
300 continuous, 2000 surge.
 
As soon as I ordered it, I noticed it wouldn’t be here until May 4. I contacted seller, she said that’s accurate. She said something about the supplier sending them to her or something. But I also noticed like you said, @dart_68 , the listing is gone. That sellers other listings all now say delivery April 15.
I don’t know what’s happening, but I think there’s some BS going on. I told the seller I can’t imagine anyone taking four weeks to ship in this day and age. As long as I get my switch. Sorry you couldn’t get one.
Also, the price was pretty good. $63
@66Valiant528, what would be a good rating for the switch?
 
Sorry I haven't been following the thread and missed a bunch of posts.
But here's a webstore I stumbled upon when looking for Packard 59 terminals
Lots of relays if thats what you're looking for.
CE Auto Electric Supply – Automotive Electrical Solutions

As far as rating. Figure if the starter power is going through it like shown in the top scheme (post 36) then it needs to be able to easily handle max starter draw. What's that? I don't know but the shop manual or the manufacture will list both 'normal' and max draws. A couple of hundred amps, not a 1000.

If going with the second scheme, then got to look at both directions on the heavier wire.
What is the max power that everything is going to draw if the engine is running on battery power? Say you have to drive it a while with a dead alternator. A car with points ignition is going to be like 3 amps maximum in the day time, plus a few amps for brake lights and turn signals etc. Probably no more than 30 amps with wipers and headlights etc. A car with EFI and electric fans is another story.
In the other direction, whats the recharge rate expected on the battery. This somewhat of a guess, but probably want the switch to be capable of handling at least 60 amps. I know that's way too high of a charge rate, but lets say a battery plate got loose and you need to kill the car. Whatever you choose, it seems logical the switch should be capable of handling more current than the maxi-fuse or fusible link on that line.
 
Thanks, Triple R. We don’t have O’Reilly’s around here. But I have plenty of other stuff to do on the car. But I will keep it in mind, if they don’t ship it when they say.
 
Thanks, Triple R. We don’t have O’Reilly’s around here. But I have plenty of other stuff to do on the car. But I will keep it in mind, if they don’t ship it when they say.
Order it inline.
 
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