GM XM Radio Kit

[Klaus]

I suspect the 24 pin connector plugged into the back of the radio. If you read the instructions, what you are basically doing is removing the positive and negative wiring from the connector, then adding the replacement positive and negative wiring from the kit, which is essentially a set of "Y" adapters to give the XM tuner power. One of the pins could be loose or bent.

The only other thing I can think of is a loose or broken fuse.

Make the dealer fix it. You paid them to install it, right?