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Old 08-12-2009, 12:09 AM   #1 (permalink)
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Battery cut-off switch wiring with EFI

Looking for a few pictures or schematics on the best way to wire in a batery cut-off switch with my build. I have the Ron Francis chassis harness, a stand alone EFI panel for my modular engine, and the battery is located in my engine bay. Battery is wired to a solenoid mounted on the firewall, where all of my power connects to (I.e. feed to fuse panel, starter, alternator and EFI panel).

I got the cut-off from another forum member but no instructions. I have also read that with a computer (and clock) you should wire in a "keep alive" circuit breaker...but not really sure what that looks like. I do understand the basic concepts. Also, with a 130 amp alternator, is it good to wire the cut-off switch in before or after the alternator feed to the battery?

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Old 08-12-2009, 12:19 AM   #2 (permalink)
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Scott,

I would wire in the cut off before battery feed from alternator then get a 10 amp self resetting breaker and wire it across the cut off switch. That is plenty of current for the computer keep alive and clock.

I mounted the battery in the trunk. You can see the back of the cut off switch with the circuit breaker mounted across the terminals.

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Old 08-12-2009, 12:22 AM   #3 (permalink)
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I wired the cutoff into the positive lead from the battery to the starter.

The "keep alive" is simply a little fused jumper between the terminals of the cutoff switch so that when you turn the cutoff switch off, there is still a small current going to your EFI computer. You want to fuse it (I can't remember what amp fuse) so that it blows in case you have to turn off your cutoff switch for some sort of "large current draw" reason (ie: emergency or fire!) or to kill all the electrics in the car (something shorted and smoking!). You can makeup your keep-alive jumper or just order one from Breeze.

Lots of people say to put your cutoff switch in the cockpit within reach...others use it as a theft deterrent and put in the trunk where you can lock the trunk after turning it off. Your call.

Make sense?
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Old 08-12-2009, 02:00 AM   #4 (permalink)
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Scott,

I didn't like the idea of installing a fused jumper between the terminals, because I knew that I would always be blowing fuses everytime I forgot to put the key back in prior to starting. Just as I thought, I've tried to start the car 4-5 times already before remembering to put the key back in the cut off switch.. I ran a 10 AMP fused hot wire straight to the keep alive wire PIN1 of the ECM. If you jumper the cut-off switch you're not really cutting the power to the car when you turn off the switch and you will still be forced to disconnect the battery if you're going to do electrical work on the car. By jumpering, you're only preventing someone from starting it.

By doing it this way, nothing happens or burns up if you try to start with the switch turned off, the ECM will always retain it's memory and you will have no powered circuits except for the keep alive wire for the ECM. Some people brought up possible issues in the Archives about back-feeding the alternator and other stuff, claiming that you could smoke something, but I have not experienced any problems. There are many others that are using this method without problems too..

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Old 08-12-2009, 03:52 AM   #5 (permalink)
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See Mk3build.com

Recommend taking a look at Mk3build.com
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Old 08-12-2009, 04:13 AM   #6 (permalink)
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I dont have a keep alive circuit, and never had any issues with my computer. I switch it off every time I park on a public lot, runs fine on restart. If the computer 'forgot', it relearned before I'm off the lot.
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Old 08-12-2009, 10:59 AM   #7 (permalink)
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Quote:
Originally Posted by BurlesonCobra View Post
... I knew that I would always be blowing fuses everytime I forgot to put the key back in prior to starting.
I used a self resetting 10A breaker...computer stays powered, still protected if there is a large draw and no fuse to replace if you forget.

BTW, on the few occasions I've tripped it I have observed the same as Rich; no noticeable difference in how the car runs after loosing keep alive memory power.

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Old 08-12-2009, 12:37 PM   #8 (permalink)
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Like Jeff, I use a self-resetting breaker: 15 A I believe, from NAPA. The resetting feature is almost instantaneous once the tripping load disappears. In my case, when I used a fuse instead of the breaker, I kept blowing that fuse by trying to start the car without having defeated the system Hella cutoff switch. No more problems.
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Old 08-12-2009, 02:02 PM   #9 (permalink)
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No battery cut-off switch here.
25,000 miles 6 seasons.
No issues.
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Old 08-12-2009, 03:20 PM   #10 (permalink)
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Quote:
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Recommend taking a look at Mk3build.com
Thanks everyone.

BTW Mark - I was trying to get on his site last night but had lost my password and no longer have the same email address it was associated to, so I regeistered for a new one. Just noticed this morning I have access to his site.
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