Thanks! I think I chose the "live" for the reason of not running it thru the firewall.

 

Plus, there are PLENTY power sources that are on, and plenty that are on
only when the car is running. You can get them right from your fuse box.

I see people asking these questions a lot, but not one person has a volt meter?
I mean, all you need do it test the fuses with the car off, note all the ones that
have power, and all the ones that do not. Then, turn the car to run, then retest
all the ones that did NOT have power with the key off. Any one that now has
power that did not, well, BOOM, there you go... Put one of those "Add a fuse"
in, and you have power...

Anyone that is going to be messing with the eletrical system should have a
test device, be it a volt meter or a simple probe with a light on it. Walmart
sells them as cheap as you can possibly get.

Using MAF, or other emissions device power lines to even trigger a relay can cause
problems with the emissions device. These lines are NOT individually fused
either. There is no MAF fuse, there is no EGR fuse, so you can either damage
your ECU, or pop the ECU fuse. I saw " these circuits are built and fused for
their current load" - Sorry, but there are no individual fuses for those emissions
devices and sensors; they are powered from the ECU. You show me in any fuse
center where there are separate fusses for MAF, EGR, O2, ECT, IAT, and so on.
Hint: There aren't any. While tapping into one of those power lines would work
to trigger a relay, it's not advisable. Of course, no WAY should you ever use one
to power a device directly.

 

I have a volt meter and use it all of the time. I was just wondering if I could tap into an ignition source under the hood near the fan adjuster. Sounds like Not I will run it to the fuse box. No problem. Thanks

 

This is a little late based on the date, but for future reference. For Ford, 12 volts key on under the hood try the "J" post (brown wire in 1967) on the starter solenoid (the small post nearest the wire that goes to the starter. This is using the Ford 4 post solenoid if they haven't changed over the years and you can find it. Just to be safe use a voltmeter to verify your voltage and that when you turn the key on 12 volts is there. This is not a fused source so wire accordingly, but it is switched (at least in1967).