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Discussion Starter · #1 ·
I've done searches and seen many other posts in one way or another try to address wiring a two post battery disconnect switch. Seems to me if you took the positive lead of the battery and the alternator wire to the same post of the battery disconnect and the output wire to the solenoid, this would kill the electric to the car from both battery and alternator thus immediately killing the engine. That to me is the safety way of doing it. If you wanted to do it because of a theft deterrent that as well as disconnecting the fuel pump (assuming you have an electric one) would work. Your thoughts?
 

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Just split the positive cable from the battery with the disconnect. If you have an EFI car, keep a jumper with a small fuse in it across the terminals of the disconnect keeping the computer hot. Simple.
 

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Opp's.. Sorry Don, Mis-read that. My cheaters are in the living room!
 

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If you don't already have the switch, check out the Flaming River disconnect switch that includes an alternator disconnect. I used one on my car as an emergency/storage switch after I heard of at least one FFR burning to the ground (with the garage) due to a short in the alternator. Quick and easy installation.
Summit has them: FLA-FR1013 $79
Not cheap, but nothing worthwhile ever is...
 

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Purple.....While I have not tested this circuit yet, this is the way I intend to wire. To prevent the potential short circuit that Dimark1 referred to, I inserted a 100A circuit breaker. This being said, I was not aware of the Flaming River disconnect noted above .... it looks like a good, simple solution - probably cheaper than the breaker+disconnect I am using.

 

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Discussion Starter · #8 ·
I take it the two side posts are for the battery connections and the center post is for the alternator? Couldn't you accomplish the same thing with a two post disconnect switch where the pos. lead from the battery and the 10 ga. wire from the alternator go to one post, then you have a 4ga. wire to the starter solenoid. Seems once you broke this circuit with the switch, you would break any/all electrical connection to the ignition box thus killing the engine.? The wire to the alternator has a fuse built in, so for safety I would only need to add a fuse to the battery lead.
 

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Looking at the diagram where is the ground to the chassis? Doh!!! Anywho run 1 fat wire to (+) to one side of the kill switch, off the other side run a fat wire (+) to the front of the car to post on mini starter, take power for alternator from same post, run small wire for fuel pump relay to switched side of kill switch. Everything will die when you turn the switch.Don't forget your memory saver jumper. Bob
 

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Discussion Starter · #10 ·
I tested my theory today, it works. Tied the postive lead of the battery AND the charge lead from the alternator to one post. I then ran another wire from the other post to the solenoid on the firewall. No juice to start (theft deterrent) and shuts off the engine immediately when turned off (safety). Switch is rated for 100 a continuous, so I think I'm ok with a 75a alternator. Will be doing the permanent installation tomorrow.
 

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Purple-

My take is that your solution accomplishes everything you (and I) want here. The only downside is that we'll have (2) heavy gauge positive wires running to the front of the car.....
 

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I added a 150 amp breaker at the battery to the circuit shown to protect the wiring and ran #1 wire to handle the current.

Charlie
 

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Purple,

Your proposal is exactly how my car is wired. The one thing to be sure of is that the leads from the alternator to the battery still have the fusable links in them. Mine do.

Someday, I'll put in the keep alive fuse separately. I don't use mine for theft...just for safety, so it stays on until I'm doing something that I would have unbolted the battery to work on it. It will indeed die when you shut it off. Not only that, but the battery load dump (term for disconnecting the battery from the alternator on a running engine) will not occur because you never disconnect the battery. Your ECU will thank you for not dumping 100V onto it's 12V line.
 

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Originally posted by Jack ffr1846:
The one thing to be sure of is that the leads from the alternator to the battery still have the fusable links in them.
In the diagram SR71 has provided, the circuit breaker bewteen the alternator and battery performs the same task as a fusbile link, albeit in a much safer way.
 
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