03 Explorer under hood source for ignition power

[buggman]

I would normally just grab a DMM & start probing wires until I find what I'm searching for but I haven't been feeling that well & standing hunched over the engine bay in the hot sun doesn't appeal to me right now, so I thought I'd see if anyone knows off the top of their head or has a wiring diagram they could share.

I'm looking for a 12v power source that only gets power when the truck is running.

I'm going to be installing a relay/solenoid style battery isolator & I need a 12v power source to trigger it to connect both batteries so they'll charge at the same time yet be isolated when the truck isn't running. That way I can power the amps from the 2nd battery (hopefully soon to be installed) and let the head unit get power from the main battery as it's a much smaller amperage draw.
I don't need a lot of amperage as I can connect a secondary relay as a trigger/amplifier if needed.

Since the radio stays on after the key is turned off (until I open the door) the radio amp remote wire won't work as I want to isolate the 2nd battery from the main battery when the truck isn't running. Also since there is not a "accy" position for the key... you have to turn the key to ON to get the radio to come on, using the head unit remote turn on won't work :thumbdwn:

I'm not as familiar with the explorer wiring as I am with my Ranger, so I thought I'd better double check things

 

[swshawaii]

Wiring Diagrams (Electrical Distribution)

http://www.bbbind.com/free_tsb.html

 

[Joe in NY]

They make panels for this exact reason... Pretty much, they are just heavy duty diodes. To allow voltage to go to the battery, but not back to where it came from.