Inside Cig lighter adaptor, Clear wire!

Hey. I wanted to put more neons in my car, but problem my new neons are not colour coded wires, both are clear on all the ones i have instead of a red and black. My question is , how do i know which on is + and -
I took the cig lighter joint bit appart so i could see and looked at the two wires in there,, has ne one had to work it out before,,,
One wire conects to a spring, which is the point on the end of the cig lighter adaptor, and the other attaches to one of the two little prong things on the side of all adaptors.
Am i right in thinking that the one attached to spring is + and the one atttached to the metal prongs on side of adaptor is - ??

Ne one who can help would be much apreciated,, dont wana blow up them all.:biggrin:

The spring contact in the center is positive and the outside shell is negative.

Thanks Craig, new there would be a simple answer.