Car intermittently loses all electrical power, when running or not. cables appear to be in good condition and are clean and tight. Everything goes, lights, ignition, dome lights, alarm system; a complete blackout

Preliminary checks to the charging system should be made regardless of the fault condition. These checks include:

• Check fuses/fuse links to the generator to make sure that they are not burned or damaged. This condition, resulting in an open circuit or high resistance, can cause erratic or intermittent charging system concerns.
• Check battery posts and cable terminals for clean and tight connections. Clean the posts and cables to verify good electrical contact.
• Check for secure connections at generator output, voltage regulator and engine ground. Also check connection at the power distribution box and harness.
• Check generator drive belt to verify proper tension and no slip between the generator pulley and drive belt. Refer to Section 03-05 .
• Check battery for full charge as described

Voltage Drop Testing the Charging System

Battery terminals clean and tight, battery negative cable clean and tight at engine block/head and chassis, Positive battery cable clean and tight at fuse box and starter. Usually have this issue with older W bodies.

It is a difficult one to answer because it is intermittent and probably will not happen during a fault finding test. Intermittent faults in electrics generally are a result of bad earths ,rusted earths , loose battery terminals and cables into the terminals ,battery posts and terminals not shiny clean, loose connections in the harness, loose fuses holders and fuses harness connecters being dirty at the contact points and an electronic unit that has an internal (ECM) fault that occurs when the road is rough, bumps . For your problem I would be checking that all the connections into the ECM are clean and the connections are tight . Battery terminals and loose wires on the alternator. And one that happens sometimes ,heavy keys hanging from the ignition switch will sway back and forth and momentarily disconnect the run circuit. IT has been known to happen . So I think to be fair to the person doing the diagnostic check it would be akin to looking for a needle in a haystack while wearing brown coloured glasses. When it happens try to be aware of the exact circumstances at the time , how long the car was in operation, weather conditions (hot-cold), What you had working at the time (radio, lights , cigarette lighter, wipers what ever). Anything may seem unimportant at the time but may point to what is happening and so help the mechanic /electriciaan

check battery cables make sure they are clean and tight and make sure the alternator charging battery. first check battery volts. should be 12.6 volts. with engine running alternator out put at battery should be 13.5 - 14.5 volts. if not either alternator failed.check alternator power feed wires and voltage regulator wires for damage or make sure electrical wires has tight connection.check alternator battery.first turn off radio before before disconnecting negative battery cable.

All the connections to the battery must be good, as they test emissions thru the OBDII system

The inertia switch will not have anything to do with this,have the alternator checked and the connections to the battery,that they are clean ,and tight,make sure the battery is good also.If this is at all helpful,please rate thank you.

If it will start after you 'wiggle' the battery cables, you don't have a tight connection. Remove the cables, clean all the connections with a wire brush, then make sure you firmly attach cables. Connections MUST be clean and tight. If you continue to have trouble, check the connections at the other end of the cables (starter and ground), as the 'wiggle fix' may be a loose or dirty connection at the other end of the cables. This is probably also the cause of your elec. problems, hopefully once connections are cleaned and tightened properly, all will be fixed.

that model year has two starter relays one beside battery and the other on the starter motor this is my suspects

Perhaps alternator is not charging the battery properly 
Test with a voltmeter - fully charged battery should read approx. 12.8 without engine running
With engine running should read 13.8-14.2 .
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Check the sparkplug wires and make sure the sparkplus are tight 
also check the two basic and very common thinks for this problem.the fuel pump and fuel filter.
if the pump is clogged and filter is dity this can occur.as when ever the fuel gets clogged ,this would make the car stall out and lose power as soon as the engine stopped sucking the fuel due to the debris .
check out this.
thanks,please do rate the solution.thank you for using fixya.keep updated.

ifi it is a problem when hot1st go to control module after checcking for ocilating curent on - side of coil