12 volt source in start & crank position

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ballajb64

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Jul 13, 2006

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Jul 1, 2009

#1

• Jul 1, 2009

• #1

I am doing a efi swap in my 1964 1/2 Mustang and I am having problems with finding a source that gives 12 volts in both the start and crank position.I was trying to use a ignition wire that was hooked up to a stereo but in the crank position it loses voltage. Would I maybe have to tap into the wire directly behind the key ignition switch?

 

67coupestang

Founding Member

May 31, 2002

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Jul 2, 2009

#2

• Jul 2, 2009

• #2

IIRC when i did my 76 bronco in efi i wound up running a relay to get the solid 12v. The relay got its trigger from a wire like your describing that dropped in voltage when cranking, but the load side came directly from the battery. not the most direct A-->B but it worked

 

golf4283

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May 30, 2003

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Orland Park, Illinois

Jul 2, 2009

#3

• Jul 2, 2009

• #3

On the back of the ignition switch is a keyed and crank 12v source. I use it to power my electric fuel pump. I forget which wire it is exactly and cause i did the Painless chassis harness color wouldn't help you much anyways. Either way though that's a good place to get the power you're looking for.

 

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v8only

Active Member

Jul 3, 2003

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Jul 2, 2009

#4

• Jul 2, 2009

• #4

directly off the backof the key switch, It may be a red wire..short a couple of inches...tap into that before it goes into the pink wire

 

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aug0202

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Jun 13, 2009

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Jul 3, 2009

#5

• Jul 3, 2009

• #5

running off the back of the ignition switch would be the most ideal place to tap into you could also use the + terminal of the coil. another thing you could do is hookup a test light to any wire and check them in both positions granted it won't tell you if you have 12 volts but it will tell you which wires are hot in those positions.

 

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v8only

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Jul 3, 2003

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Jul 4, 2009

#6

• Jul 4, 2009

• #6

the + side of the coil will provide constant 12v source, and not key on/start. the only single source of both key on and start is that ignit switch. otherwise, you'll provide a constant 12v source to whatever it is you're wiring up

 

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2+2GT

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Apr 25, 2009

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Southeastern Pennsylvania

Jul 4, 2009

#7

• Jul 4, 2009

• #7

The ignition switch is not intended to provide power to the coil during start. There are two small posts on the solenoid. The one nearest the battery (S) is the connection from the ignition switch to activate the "START" circuit. When activated, the other small terminal (I), nearest the firewall, provides a full 12V, bypassing the resistance wire, to the coil, with the key in the "START" position. This function is part of the engine wiring harness. No point in re-inventing the wheel, this is where starting voltage is intended to come from. A pretty good design, it would be hard to imagine a better source for full 12 volts during the start.

 

Tim65GT

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Feb 24, 2004

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Jul 4, 2009

#8

• Jul 4, 2009

• #8

A pretty good design, it would be hard to imagine a better source for full 12 volts during the start.

Click to expand...

True, but the OP was asking about a point for 12 volts in both the start and crank position.

As golf4283 stated, at the igniton switch the C (coil) terminal should remain 12V during crank. It's possible the 64 1/2 models do not. In that case you will have to wire up a relay as 67coupestang stated.

 

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2+2GT

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Apr 25, 2009

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Jul 4, 2009

#9

• Jul 4, 2009

• #9

Tim65GT said:

True, but the OP was asking about a point for 12 volts in both the start and crank position.

As golf4283 stated, at the igniton switch the C (coil) terminal should remain 12V during crank. It's possible the 64 1/2 models do not. In that case you will have to wire up a relay as 67coupestang stated.

Click to expand...

No, this provision is identical in 64 to the later models.

I fail to see any difference between "crank" and "start", since the switch "cranks" the engine only during starting. The switch is marked "ACC OFF ON START". If he needs power during "ON", there are at least a dozen good sources. Or if he wanted full-time clean power, go direct to the battery terminal on the solenoid. That's what Ford did for convertible top power.

He spelled it out for us. The solenoid connector is intended to provide a clean 12V during starting, with as little voltage drop as possible, which would not be the case under the dash, which he complained about "I was trying to use a ignition wire that was hooked up to a stereo but in the crank position it loses voltage."

 

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v8only

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Jul 3, 2003

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Jul 4, 2009

#10

• Jul 4, 2009

• #10

name a spot where he can get voltage during crank and on at the same time, but turns off with the key off other than the ignit switch.

 

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2+2GT

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Apr 25, 2009

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#11

• Jul 4, 2009

• #11

v8only said:

name a spot where he can get voltage during crank and on at the same time, but turns off with the key off other than the ignit switch.

Click to expand...

Huh?

 

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v8only

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Jul 3, 2003

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Jul 4, 2009

#12

• Jul 4, 2009

• #12

the original poster wanted a 12v source that was a steady 12 during both crank AND run... although I could be wrong, but on an early car, the ignit switch is the only source I can think of...