aux outlet fuse keeps blowing..?

hey, not sure about year model but it may be a cigarette lighter. the two are different in that the lighter has metal prongs that hold the element in place till it gets hot.Plug in an accessory and the ground springs will contact the prongs, shorting out the fuse

I recently had a problem with the back up lights due to a small nick in the insulation of wires in trunk - no doubt I tried to stuff too much in the trunk and caused the problem. The short was causing fuses to blow, affecting the transmission to the point that it wouldn't shift. Almost replaced the transmission before a mechanic found the problem. Interesting thing was, that I'd checked the fuses, and didn't look blown - but who would expect back up lights to be blowing a fuse regulating the transmission?