Gary's suggestion will get you started, however; most cars will light a test lamp as they draw current all the time to run the clock, security system, OBD, etc.. They don't draw a lot, but they will cause a test lamp to glow. You've got something drawing substantial current and you'd be better served with a multi-meter that measures current (amps). You can then pull fuses and find the circuit that is drawing a lot of current and work backwards from there. A likely culprit is a stuck switch (or relay).

As to the Tacoma - might just be the crappy oxygenated gas that's mandated in the winter months..

Good luck and let us know what you find..
Glenn