Goatman sez check and/or replace the alternator brushes. A good idea. Labor is the same when you pull them and check and the install them or install new set. I have usually put a new set in, and kept the old one if it's useable.

NOTE: job is easily done on the car if you have a power screwdriver and the oil filter is removed, as during an oil change. Disconnect the battery, too.

Your important clue is that only the oil light came on. That light is wired separately from the others insofar as the method of its ground side. Its power side is the same as the others, its ground is through the oil pressure sensor. Pressure too low and the light comes on.

The power to the sensor gets to it via the small black wire that you should see, along with a small red and a large red, coming up between the alternator and the block.

That small red wire is your main suspect as to battery being dead and the ALT light being on at the wrong time.

When the key is turned to Position II, before starting, that is the "bulb check" position. Power from the key flows to the warning lights, and the ALT light grounds through the alternator rotor windings.

The route is from the dash to that gray connector on the firewall. From there it is a red wire inside the main harness to a branch harness that goes under the front of the engine coming up and connecting to one alternator brush. The path is through the rotor windings and out to the other brush, which is grounded.

There is a small current flow through the rotor (called excitation voltage), just enough to make a magnetic field enough to make a little electricity when the rotor turns. As the spinning increases, the ground becomes positive and so the ALT light has no ground and it goes out.

IF that light is on when the alternator is spinning it means that the red wire is grounded somewhere else, and the alternator will not start charging so the battery dies.

The easy fix is a new red wire from that gray connector to the alternator, routed along the RF fender with a lot of slack to the alternator to allow for engine movement.

Long post I know, but I just can't pass up a "teaching moment",

Good Luck,

Bob

:>)