On Thu, 15 Mar 2007 15:34:25 -0800, Jim Stewart
wrote:

They don't typically have an A&P rating do they?
By what authority do they sign off repairs and
how do they get that authority? I haven't been
able to find anything specific to avionics in
FAR/AIM.

The ones I know either work for a Repair Station and so the authorized
avionics inspector signs the work off under the station's licence, or
they have an Airframe rating.