If you are refering to the warning lights on the dash, the alternator is the culprit. Either a wire is loose at the battery or the brushes are worn out.

Your car will run on battery power only for a little while, especially with the day time running lights on.
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My name is Klaus and I am a V♂lv♂holic

I would suggest that we get a better description of the problem.

By "lose all power" what do you mean? Some people might refer to "power" as electricity. Others refer to it as the power from the engine. Are you saying the the engine stalls completely and you have to restart the engine?

By dash lights coming on and going off and then they stay on when you lose power, is it simply possible that the engine has stalled and the dash lights that are coming on are the same dash lights that are on when you first turn the ignition key to start the car?

Are we looking at an ignition switch problem here?

Smetty - try posting this as loss of power but don't forget to mention the lights.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '72 Yamaha Rd400, '68 Honda 350-4, '12 XC70, the first 5 are mine, heh, heh, 525,000 miles put on 10 bricks James A Sousa

This sounds like my '90 744 TI that would stall when I put the high beams on.

The solution is in the 700/900 FAQ - the problem lies in the grounds in the left front fender.

The headlights on a 740 (and other things) ground in the left front fender as well as the power stage for the ignition. When the high beams draw more power, they overload a poor ground and kill the ignition.

i suspect that your problem is similar - check and clean all the grounds in the left front fender and those for the ignition.

Any item that does not have a ground wire probably gets its ground through its mounting - clean its mount.

The dash lights are probably lighting because the headlights are back feeding through them because their ground is bad.

Many unusual electrical problems can be traced to bad grounds.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '72 Yamaha Rd400, '68 Honda 350-4, '12 XC70, the first 5 are mine, heh, heh, 525,000 miles put on 10 bricks James A Sousa

I would think it's either the light switch itself or the relay (if there is one).