I need to "power up" an accessory which is located under the hood. The ground is no problem but the hot lead(red) must be live only when the engine is on. Does anyone have any suggestions as to where I should connect to?

 

You'll have to tap into the ignition power most likely, where that is under the hood, I don't know. You could run a wire from inside the car, behind the headunit or from the fusebox through the grommet behind the battery up into the engine compartment?

 

good luck

 

Thanks Anyone else with a suggestion?

 

The under-hood fuse box is there because it has circuits that DON'T go through the ignition switch, which is why it's tough to find an ignition wire up there.

There is one exception - the ELD unit. It is a sensor that measures the electrical load, and it's switched on and off by the ignition switch. If you look at this photo you'll see a 3-wire connector near the lower right of the fuse box. That's the ELD sensor, and the black/yellow wire on that connector has +12v controlled by the ignition switch.

If your accessory only uses an amp or less, go ahead an tap into the black/yellow wire, but make sure you use an in-line fuse. If you blow the 15-amp fuse that feeds this circuit you'll lose half the electrical stuff in the car (alternator, gauges, oxygen sensors, and numerous emissions systems).

If your accessory uses more than an amp, I'd suggest installing a relay in the under-hood fusebox, activated by the black/yellow ELD wire. Use the terminal marked "+12v" in this photo as your +12v source for the relay contacts, but again be sure to use an in-line fuse. This +12v terminal is connected directly to the battery.

 

Thanks MODIFRY... Your the Best!