The antenna lead is a coaxial type cable. This means that there is an inner conductor (usually a solid copper wire, then there is and insulator around that inner wire. Around the insulator is a braided conductor, and then the outer covering. You need to solder the inner conductor together and then provide some insulation. Then you need to solder the outer braided conductor together so that it doesn't make any contact with the inner conductor. Then insulate the whole connection. If done carefully this will work. There are some good pictures and additional instructions at this link. http://goldwing.eurekaboy.com/shortencoax.htm
Thanks to Eurekaboy.
I don't know what xm you have, I have a skifi2 and I found complete car kits at delphi.com for only 9.99 includes complete kit with antena, I don't know if this will help since I don't know what unit u have howie