Live wire when ignition switched on!

[Maree74]

1997 standard Ford Explorer
4.0 SOHC

I'm hoping to find a +12v connection only when the ignition is switched on.

I've had the fuse box out and opened but I'm unsure where to take my connection from!

Can I make use of one of the 'unused' fuse locations eg. 9, 30, 35, 36, or take a lead off one of the other (ignition on) live fuses?

Rated current is 15 Amps.

Anyone know the answer ? (I could always take a direct line from the battery and stick an inline fuse in?)

Thanks

 

[J_C]

How much current do you need to draw? Was that the 15A you mentioned?

I'll edit this post as I look at those fuse positions, or you'll reply, whichever comes first. Is it acceptable for the circuit to be powered in both run, and accessory key cylinder positions? Do you have the means to connect wire to the contact on the unused fuse positions if there isn't one already?

Some of those fuse positions were originally rated at 7.5A rather than 15A, so I'd check to see if there are existing wires and if the gauge is low enough to handle (15A?) what you need.

Do you have a multimeter? Using one you should be able to tell if those fuse locations are only live in run or accessory mode? Suppose they all are, and aren't live with engine off and/or after the battery saver circuit times out, then pick which you're most certain you'd never want to use for the original purpose. #30 is park lamp/trailer-tow relay, already rated for 15A. #35 and #36 are for EATC blower, and other features that are apparently not on your trim level of vehicle. Both of those when powering factory equipment, had a 7.5A rating, but both are more likely to cut off when the vehicle is off and fully timed-out from the battery saver circuit.

Since 15A is a non-trivial load, it would be better to use one of those unused fuse positions rather than tap into some other circuit and expect it to have an extra 15A margin in it.

Otherwise, there are 2nd gen wiring diagrams linked in my sig below and practically all of them, show at the top of the page, the fuse #'s of the circuit and when it's live.

 

[Maree74]

How much current do you need to draw? Was that the 15A you mentioned?

I'll edit this post as I look at those fuse positions, or you'll reply, whichever comes first. Is it acceptable for the circuit to be powered in both run, and accessory key cylinder positions? Do you have the means to connect wire to the contact on the unused fuse positions if there isn't one already?

Hi, the 15 amps is the rated current, I think reality is much less. At the moment nothing seems to run in accessory key position, so, I only need it in the run position in reality. I had a look at the internal fuse panel today and found this to be a possible problem as I couldn't properly see a connection on the unused fuse points. I would have to remove a couple of panels to get better access if this is what would be required.
I know that I can get a power supply for this unit but it is less than ideal as it would mean introducing a switch in the circuit, this comes with the problem of it being left running without the engine on - hence the need for a live line only when the engine is running.

 

[J_C]

You can tap into just about any circuit that's live with engine or accessories on, and not worry about how much current you're asking of the circuit, by only using that circuit to power a relay, take circuit to relay coil A, take relay coil B to ground. Then put a series fuse from the battery, go through the relay to the powered load.

Won't you have to take panels off to get access to anything to tap into?

What are you powering, an amp? I mean if it's aux lighting then wouldn't you want a switch on it anyway to turn off when driving public roads? If it's an amp then I'd use a relay as described and take the power feed to the radio as the relay trigger. The multiple radio wiring diagrams are among those linked in my sig, all of them having fuse #20 on the interior panel, only live in run or accessory mode. This would only be to power a relay, as it's only a 7.5A rated circuit.

 

[Maree74]

You can tap into just about any circuit that's live with engine or accessories on, and not worry about how much current you're asking of the circuit, by only using that circuit to power a relay, take circuit to relay coil A, take relay coil B to ground. Then put a series fuse from the battery, go through the relay to the powered load.

Won't you have to take panels off to get access to anything to tap into?

What are you powering, an amp? I mean if it's aux lighting then wouldn't you want a switch on it anyway to turn off when driving public roads? If it's an amp then I'd use a relay as described and take the power feed to the radio as the relay trigger. The multiple radio wiring diagrams are among those linked in my sig, all of them having fuse #20 on the interior panel, only live in run or accessory mode. This would only be to power a relay, as it's only a 7.5A rated circuit.

Thanks for the info J_C: I think this is just what I'm after. It is one of the after market screens with amp and maps and cameras etc. It was on the vehicle when I got it but the power supply has since gone dead (though everything else is working) so that's why I'm linking in a separate supply.
The solution you've given looks good and achievable.
Roy

 

[Maree74]

Thanks for the info J_C: I think this is just what I'm after. It is one of the after market screens with amp and maps and cameras etc. It was on the vehicle when I got it but the power supply has since gone dead (though everything else is working) so that's why I'm linking in a separate supply.
The solution you've given looks good and achievable.
Roy

Hi, have done a fix with a relay as you explained and everything is now working. Just want to say thanks for sharing your expertise...

 

[J_C]

Good to know it's working and thanks for completing the topic!