Switched 12v - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 14 (permalink) Old Apr 13th, 17, 11:17 AM Thread Starter
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Switched 12v

I need to find a clean switched 12v source to wire in my Sniper efi. I have something on the ign terminal on the fuse box. It needs 12v during cranking as well. This is on my 70 Chevelle with stock wiring. Sorry I'm just not that confident with this stuff. If anyome could point me in the right direction, I'd appreciate it.

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post #2 of 14 (permalink) Old Apr 13th, 17, 11:55 AM
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Re: Switched 12v

When I wired my MSD box up I used the original coil + wire.

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post #3 of 14 (permalink) Old Apr 13th, 17, 12:04 PM
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Re: Switched 12v

The ignition terminal on the fuse panel should have power during cranking as well.

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post #4 of 14 (permalink) Old Apr 13th, 17, 12:36 PM Thread Starter
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I'm running a wire from the ign terminal on the fuse box to a relay. That is powering my HEI distributor. So that's already being used.
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post #5 of 14 (permalink) Old Apr 13th, 17, 1:13 PM
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Re: Switched 12v

You can still use the IGNITION terminal, it will support more than just the HEI feed current levels. (On this, I am assuming the wire you need the current from, is much like an MSD operation wire, simply turns the Sniper system on and off? If so, no problem with using the IGNITION terminal, with the HEI).

When I run an HEI that I do, idle uses 3.5 amperes, red line, 1.3 to 1.5 amps total. Difference is tht at lower rpm's, there is more time in milliseconds for the coil to saturate, than at higher rpm levels, so, idle, more amperage use, red line, significantly less.
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post #6 of 14 (permalink) Old Apr 13th, 17, 1:13 PM
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Re: Switched 12v

Run a larger wire from the relay to a bus and use it as a switched source for the HEI and other applications.
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post #7 of 14 (permalink) Old Apr 13th, 17, 1:41 PM
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Re: Switched 12v

Quote:
Originally Posted by 70CHEVELLE396 View Post
I'm running a wire from the ign terminal on the fuse box to a relay. That is powering my HEI distributor. So that's already being used.
It's easy enough to solder or crimp two wires to a single terminal as long as you don't exceed the amperage rating of the fuse which you won't be. You will have no issues if you do that.

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post #8 of 14 (permalink) Old Apr 13th, 17, 1:52 PM
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Re: Switched 12v

As Dave alluded to, the first thing we need to verify is, that this is simply a "trigger" wire with low current demands. If it is, then there is no issue with connecting on to the IGN slot on the fuseblock,
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post #9 of 14 (permalink) Old Apr 13th, 17, 3:21 PM Thread Starter
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Ok sounds real good. I'll look into the demand for the Sniper system on that 12v switched lead (pink) wire. It also has a direct connection to the battery, so it most likely telling the system it's time to work! I do know through out the directions and any where you read, it's overly stressed that you have a "clean" source, and not to share circuits. Not sure if it's Holley's way to cover there butt, or if it's for good reason.
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post #10 of 14 (permalink) Old Apr 13th, 17, 4:35 PM
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Re: Switched 12v

If you can run 2 wires off the same terminal you can pick up some of these.

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post #11 of 14 (permalink) Old Apr 13th, 17, 5:20 PM Thread Starter
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Thanks Hank, I do have some of those.
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post #12 of 14 (permalink) Old Apr 13th, 17, 7:57 PM Thread Starter
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Re: Switched 12v

Quote:
Originally Posted by Dave Ray View Post
You can still use the IGNITION terminal, it will support more than just the HEI feed current levels. (On this, I am assuming the wire you need the current from, is much like an MSD operation wire, simply turns the Sniper system on and off? If so, no problem with using the IGNITION terminal, with the HEI).

When I run an HEI that I do, idle uses 3.5 amperes, red line, 1.3 to 1.5 amps total. Difference is tht at lower rpm's, there is more time in milliseconds for the coil to saturate, than at higher rpm levels, so, idle, more amperage use, red line, significantly less.
Actually all it's doing is powering the relay. The relay then gets full battery voltage off the horn relay, and that powers the HEI.

70 Chevelle, Vortecpro 496, TH400, Moser 12 bolt, custom Tom's Eaton posi, 3.73, UMI/Viking front suspension, PMT rear. Sniper efi, RobbMc PowerSurge.
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post #13 of 14 (permalink) Old Apr 14th, 17, 1:02 PM
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Re: Switched 12v

I am a very firm believer in NOT USING RELAYS for anything, just another problem to work around when they go bad, regularly.

Although the IGNITION and IGN terminals are housed in the fuse box, they are NOT fused. I have run as much as 20 amperes load off them, with no adverse effects, including multiples of things like MSD power on switch, EFI power on (Holley and other systems), electric chokes, and other things they are needed for.
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post #14 of 14 (permalink) Old Apr 14th, 17, 1:55 PM
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Re: Switched 12v

Quote:
Originally Posted by Dave Ray View Post

Although the IGNITION and IGN terminals are housed in the fuse box, they are NOT fused. I have run as much as 20 amperes load off them, with no adverse effects, including multiples of things like MSD power on switch, EFI power on (Holley and other systems), electric chokes, and other things they are needed for.
I think you need to clarify Dave.

The "add on" slots readily accessible from the front side of the fuse block with the rest of the fuses are fused. For example, talking 1970 here, the IGN slot is protected by the turn signal fuse.

If you go in thru the other side (i.e. remove the original points ignition resistance wire to install a regular wire) at the bulkhead connections, then that ignition feed is NOT fused.

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