Old Smokey has certainly hit the nail on the head, and indeed when INS equipment (and FMS's as well) were added at the customers request on the L1011, the attitide information was hardwired directly from the respective INS unit.
In addition, complete rad/nav switching was available for both pilots, to select the operative equipment.
The standby horizon is powered from the DC standby bus which, if all other electrical systems failed, would be directly conected to the battery bus, supplied by the ships battery.
Some operators, especially those that operated long overwater routes, provided two ships batteries, for added redundancy.
In 26 years of operating the 'ole Lockheed tri-motor, the ONLY item in the electrical system that failed (very infrequently) was an engine driven intregrated drive generator, and when it did, it was disconnected from the engine by the Flight Engineer.
Lockheed.....works GOOD, lasts a loooong time.
Ah Lockheed!!
