Constant 12v power source

[haskett]

Help! I'm looking for a constant 12v power source under the dash.

I'm finding that what Ford likes to label on their wiring diagrams as "hot at all times" is in fact really "hot at all times except when the starter is engaged". :nonono:

I need a power source that is hot at all times. When the starter is engaged, when the key is out of the car and all other positions in the ignition module. Surely somebody out there has figured this out when installing a radio or other accessory? Or maybe someone is better at reading the Ford wiring diagrams than I am. Ideally I would tap into a fuse, but I can't find any in the central junction box.

This was really easy on my wife's non-Ford vehicle. Thanks in advance for your help!

 

[Blueline]

There should be a few fuses in the fuse box that have power all of the time. Just throw a test light up there with the key out and see which fuse has power, then see what its for. For the life of me I cant remember which one has a constant 12v, Ill post it if I remember.

 

[SnakeBit]

What about the cig lighter? Pull the boot ring and tap into that wire.

 

[SVTgsxrdude]

What about the cig lighter? Pull the boot ring and tap into that wire.

This one^^^

 

[AlwaysBoosted]

What about the cig lighter? Pull the boot ring and tap into that wire.

This

 

[Carbd86GT]

What about the cig lighter? Pull the boot ring and tap into that wire.

+1

This is the one to use.

 

[SlowSVT]

That may be hard to overcome. Engaging the starter motor pulls mongo currant from the electrical system resulting in a voltage drop momentarily killing your accessory.

 

[08mojo]

you could go directly to the battery and use an inline fuse

 

[ruthless]

The only power I found that is key on and doesnt cut out with the starter is in the passangers side kick panel. I used this as a source to triger a relay for all of my gauges and my wideband. I go sick of everything doing a on, off and back on every time I started the car.

 

[SlowSVT]

you could go directly to the battery and use an inline fuse

That won't work. On "start-up" the battery is the only source of power and the voltage reading will be the same throughout the system.

 

[Saleen4971]

That may be hard to overcome. Engaging the starter motor pulls mongo currant from the electrical system resulting in a voltage drop momentarily killing your accessory.

If your battery is good, the voltage shouldn't drop enough to kill most 12v accessories.

Sent from my MB860 using Tapatalk 2

 

[08mojo]

I need a power source that is hot at all times. When the starter is engaged, when the key is out of the car and all other positions in the ignition module.

That won't work. On "start-up" the battery is the only source of power and the voltage reading will be the same throughout the system.

:shrug: Since the battery is the only source of power, why would it matter what wire he taps into because they all see the same voltage drop with the starter engaged. Unless he does not need at least 12V...

Perhaps the OP can tell us what he is trying to install?

 

[SlowSVT]

If your battery is good, the voltage shouldn't drop enough to kill most 12v accessories.

Sent from my MB860 using Tapatalk 2

That depends what the voltage range of the accessory. Some may operate down to 6V and as high as 24V. Others can't tolerate a large voltage swing and will "drop-out" much sooner. Why do you think the lights dim when engaging the starter?.......voltage drop.

I often use auto-ranging power supplies in the equipment I design that can use either 220 VAC/50 Hz or 110 VAC/60 Hz for international markets. I had a re-seller located in the Russia inquire whether or not our xDSL equipment would work down to 60 VAC :uh oh: because the power plants and grid was so over taxed the voltage would spike in both directions :nonono: I told him we were only good down to 90 volts.

 

[SlowSVT]

:shrug: Since the battery is the only source of power, why would it matter what wire he taps into because they all see the same voltage drop with the starter engaged. Unless he does not need at least 12V...

Perhaps the OP can tell us what he is trying to install?

Never stated that it does. The voltage reading will be the same on the 12V bus regardless where it's measured from.

In the owners manual they may list the voltage range. Most electronics operate between 3 and 5V but some components may require 9 and 12V.

A friend of mine who designs power supply told me you can get spikes as high as 50V the moment the contact with the starter windings is broken collapsing the field. The winding in the starter is basically a big ignition coil. Works in the other direction having to saturate the winding when engaging the starter (it's called "in-line currant rush").

 

[SlowSVT]

This may be a solution for the OP if he needs it bad enough to spend $139

12V line conditioner

interVOLT 12VDC - 12VDC Isolated Switchmode Power Conditioner products, buy interVOLT 12VDC - 12VDC Isolated Switchmode Power Conditioner products from alibaba.com

 

[Ralo]

Didn't read above but if your a coupe you can use the fuse slot for the convertible top. I have my radar detector wired to mine.


Edit: just read it needs to have power ALL the time. That vert switch only does when the key is on.

 

[haskett]

I've been out of town and finally got home yesterday to mess with this today. Thanks for all of the great replies.

FYI, I'm wiring a navigation computer for my open road racing. Just in case I have to hit the starter during a race (it happens), I don't want the computer to reboot and lose everything.

Here's what I found... The "hot at all times" leads really are hot at all times, as Ford advertises. The problem I was having was that the voltage would drop to 9V during the starter cycle. While the computer was fine with 9V, my touchscreen was not. The touchscreen would cycle off during the voltage drop. When the computer was sensing the touchscreen going dead, the computer automatically shutdown.

I have performed surgery on my touchscreen and it now stays alive during the start cycle. The power adapter had a resistor in it. I found another power adapter lying around that had no internal resistor, and everything now works. I have my touchscreen going to the cig adapter and the computer is hooked up to fuse 20 for switched power and fuse 33 for unswitched power.

For future reference, here are the unswitched 12v fuses that are hot at all times... 9, 13, 15, 27, and 33. My testing also indicates that 19 might be unswitched.

 

[03 DSG Snake]

I've been out of town and finally got home yesterday to mess with this today. Thanks for all of the great replies.

FYI, I'm wiring a navigation computer for my open road racing. Just in case I have to hit the starter during a race (it happens), I don't want the computer to reboot and lose everything.

Here's what I found... The "hot at all times" leads really are hot at all times, as Ford advertises. The problem I was having was that the voltage would drop to 9V during the starter cycle. While the computer was fine with 9V, my touchscreen was not. The touchscreen would cycle off during the voltage drop. When the computer was sensing the touchscreen going dead, the computer automatically shutdown.

I have performed surgery on my touchscreen and it now stays alive during the start cycle. The power adapter had a resistor in it. I found another power adapter lying around that had no internal resistor, and everything now works. I have my touchscreen going to the cig adapter and the computer is hooked up to fuse 20 for switched power and fuse 33 for unswitched power.

For future reference, here are the unswitched 12v fuses that are hot at all times... 9, 13, 15, 27, and 33. My testing also indicates that 19 might be unswitched.

Which location did you use? I need a constant 12v for my Homelink mirror.

 

[JustaGT]

go to the ignition harness

 

[Silver2003Cobra]

I know that my radar detector, plugged into the cigarette lighter will stay on, as long as their's power to the battery.. and since it's a high amperage circuit, should provide plenty of juice for your computer.