Switched 12v

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H/O84

Greasemonkey
Nov 29, 2016
181
28
Hey guys,
I need to find a 12v source that of live with the key on to use for a relay trigger for my electric fuel pump. Having trouble finding one to use. It's an 84 Hurst olds with cruise control and ac taken off and the computer has been deleted. Anyone know a good source?
 

81Regal

Royal Smart Person
Apr 5, 2009
1,523
83
Terril Iowa
Go from the fuse box, there is several switched terminals there.
 
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H/O84

Greasemonkey
Thread starter
Nov 29, 2016
181
28
I tried to find one last night but I couldn't get anything to read 12v. Do you know which fuse I might be able to use?
 

DRIVEN

Geezer
Apr 25, 2009
6,977
113
*CENSORED*
Stolen from the internet: Any of the terminals marked "ign" should be what you're looking for.
fuseboxlayoutcopy.jpg
 

565bbchevy

Geezer
Aug 8, 2011
7,941
113
Michigan
I would only use a switched 12 volt from the fuse block to trigger a relay large enough to handle the load of the fuel pump.
Also consider wiring to an oil pressure switch.
 

81Regal

Royal Smart Person
Apr 5, 2009
1,523
83
Terril Iowa
I would only use a switched 12 volt from the fuse block to trigger a relay large enough to handle the load of the fuel pump.
Also consider wiring to an oil pressure switch.

Also an in line fuse coming off the fuseblock.
 

64nailhead

Goat Herder
Supporting Member
Dec 1, 2014
2,063
113
Upstate NY
Hey guys,
I need to find a 12v source that of live with the key on to use for a relay trigger for my electric fuel pump. Having trouble finding one to use. It's an 84 Hurst olds with cruise control and ac taken off and the computer has been deleted. Anyone know a good source?

Driven's picture shows ignition pins. But you don't want your fuel pump running in that manner. You want it to run only when the motor is running. 565 mentioned using an oil pressure switch with the idea being that if there is no oil pressure, then your fuel pump will be shut off. I prefer a source that is on only when cranking and hte motor is running. That describes the 12v source for the distributor, generally the pink wire at the cap. I believe that the IGN labelled points in the fuse panel are hot when the key is in the run position - but I might be mistaken and someone can correct me if I'm wrong.
 
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Reactions: 565bbchevy

565bbchevy

Geezer
Aug 8, 2011
7,941
113
Michigan
Also an in line fuse coming off the fuseblock.
I like having full control over my fuel pump so I have mine hooked up to a Painless rocker switch. I have all of my electrical add ons wired into two 12 circuit accessory fuse panels (1 battery and 1 ignition.) each with their own blade type fuse and relays for the high amp draw items but if you are tapping into the stock fuse block then I would add an inline fuse.
 

454GrandPrix

Master Mechanic
Jul 27, 2016
429
93
Lehi, Utah
Also consider wiring to an oil pressure switch.

565 mentioned using an oil pressure switch with the idea being that if there is no oil pressure, then your fuel pump will be shut off.

Don't bother going through this needless complexity. Your carbureted engine can run for quite a while just off the fuel in the float bowls. How do I know? Because on more than one occasion I have hopped in my car, started the engine, and driven away... when I forgot to turn on my electric fuel pump (controlled by a hidden switch). After a couple minutes of run time, the engine starts to sputter and cough as it finally runs out of fuel. If I had no oil pressure for those two minutes, that would be plenty of time to cause engine damage, especially if I blissfully assumed there was oil pressure simply because my engine was running. Thus I say don't bother.

As for me, I power my fuel pump from the fuse block as described in this thread. I did put a small inline fuse right next to the fuse block, then ran this (low power) wire to a relay. This voltage activates the relay, which then passes (high power) battery voltage straight to the pump itself. This high-power line also has a fuse right next to the battery, of course.
 
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