1996 Mercury Sable electrical problem with Sable

My '96 Mercury Sable has been "babied" it's who life, but now intermitant electrical problem has dealer and myself baffled. Here's the problem:

Occasionally while driving, all the dash lights go on and the vehicle looses power. Exactly as if the battery has been disconnected and the ignition turned off. Radio turns off and presets are lost, clock goes to noon, all dash lights and warning lights go on simultaneously (similar to when key is first turned), engine off with no power, no power steering etc.

It lasts a few seconds at most and then powers back up -- but with clock at noon, radio preset lost (and power steering gone until I shut the car off and restart).

Sometimes I thick I hear a click /spark / snap noise when this occurs. Alternator and voltage regulator (one unit) was replaced 15k ago, but this problem is new and may or may not be related.

The dealer thought the ignition was bad and replaced the ignition. Apparently that wasn't the problem.

Your help or advice will be greatly appreciated.

Thanks in advance,
Tim Williams
morebarn@juno. Com