If yours is broken.. you'll have to get a new plug.. I used the Motorola ones cause I know they fit.. on my aftermarket
You will have to strip bout 3" off the first black insulation.. then you will see a braided style wire that covers everything.. that is your ground... push that all the way back to where you have stripped the rubber off.. you will see another *usually white or clear* rubber insulation.. carefully strip bout 2" off that and you should see a core wire.. some are single core.. some are multi strand.. push that thru the nipple of the plug.. bend the end over and put a bead of solder to hold it in place.. now you want to make sure the ground wires are rolled nicely enough that they are tucked under the plug hole.. and use a good amount of solder to hold it in place.
P.*. Almost forgot.. before you strip the wires and such.. get a shrink tube that will fit over the antenna plug first and put that over the wires before you commence stripping and the steps above. When you're done.. heat shrink the tubing so it grasp the plug and the wire where you did all the soldering and such.. you may want to have the plug cool down first before doing that since all that soldering would make the plug warm and as soon as you try to fit the heat shrink tubing over the plug.. it will start to shrink immediatetly and not give you enough time to cover enough of the plug to give it a good grip and coverage.