For Christmas I was given one of these Interstate rechargeable flashlights (http://www.interstatebatteries.com/c...IG8051+LIG8051)).

Yesterday I wired it into a 12v plug that I added behind the dash a few years ago to accommodate my XM radio and GPS charger. The plug is wired in using one of those "add a circuit" kits. The outlet is wired so that is keyed to the accessory or on positions, and has been working perfectly since 2010.

After installing yesterday I noticed that my battery went dead pretty quick while I was just putzing around in the driveway, but I didn't think much of it. This morning the battery was irrecoverably dead, so I went and got a replacement (my old one was 4.5 years old anyway). I installed the new one and everything started up fine. I then noticed that the radio was staying on even when the key was removed from the ignition and the door opened. Further troubleshooting made me realize that the red LED indicator on the flashlight charger remained lit even when no power was applied, as long as the flashlight was plugged in. If the flashlight was removed, the LED goes out. As soon as I unplug the flashlight, the radio shuts off immediately.

It's almost like some power is being backfed which is somehow messing with a relay or another fuse (Just typing this out, I'm wondering if the "add a circuit" is piggybacking on the radio circuit and causing the issues - I will check that tomorrow). I like the flashlight and feel bad returning a gift, but is there any type of device I can get that would stop the backfeeding of power?

Thanks,
Brian

 

Use a diode.

 

Thanks for getting back to me on this. What would be the best means of wiring in that diode? Also, what type of diode would I choose?

Sorry, I'm new when it comes to this stuff.

 

eliminates the possibility of a backfeed....

the size diode will be based on what current the charger draws