I am installing an XM satellite radio in my 94 E320. There are 3 power leads to the receiver.
1. Yellow for positive (took 12v from the cig lighter).
2. Black for ground.
3. Red, the connection for which is described in the instruction manual as: If this unit is installed in a vehicle that does not have an accessory (ACC) position on the ignition switch, the red lead should be connected to a terminal coupled with the ignition switch "On/Off" operations. Failure to do so will cause the unit to drain battery power if left unattended for an extended period.

Where do I find a terminal "coupled with the ignition switch "On/Off" operations"?

regards,

Mark