A 99 Legacy Outback 2.2 swap I did awhile back, started draining the Battery.  The new owner went to Autozone and they sold him an Alt.  He also got a new Walmart battery.  Power was still draining, the ABS light ....

 

I removed the Autozone Alt and installed a Subaru Alt.

I charged the Battery

 

It started and stopped just fine many times.  All power was removed each time I shut it off.

 

I think the main relay may have been sticking, all though I've never seen that before.

 

I looked under the dash, lower panel removed.  I did not see the relays, where are they on a 99?

 

Thanks Larry

Stuck way up in the left upper corner of the firewall behind the dash.

 

Any aftermarket stereo that could be staying on?

 

Do a draw test and start pulling fuses.

Is the parking light switch on?

No, it was not the usual things.   The Dash light ABS was on.  If it comes back, I'll dig under the dash and find the main power relay - key on, power on relay.

Thanks, Larry

If it happens again, check the ABS relay at the ABS pump. They go bad and stay on after the car is shut off at times.

Thanks, 

Larry