Sirius XM ( SIRI ) shares have plummeted as concerns mount over the fate of the Big Three automakers, but the satellite radio provider's revenue is not as closely tied to Detroit as the market seems to be indicating. Sirius XM shares are trading below 20 cents a share, as investors are pricing in the likelihood that a bankruptcy filing by General Motors ( GM ), Ford ( F ) or Chrysler will probably drag Sirius XM down as well. The company leans on the vehicle installation side of its business, referred to as original equipment manufacturer, or OEM, is key to the company's success as a merged unit. But while the long-term growth of Sirius XM is clearly closely tied to auto sales, the combined company is less reliant on any single automaker than they were before the Federal Communications Commission approved the long-awaited merger in July.