check engine light

I had it happen in mine too because of the gas cap. To reset the check engine light, as soon as you turn the key,pump the brakes hard 3 times. That fixed mine. Though it always reappears.

It sounds like your Ignition switch is defective and not completely turning off. here is some info about the light when it is on while driving http://repairpal.com/check-engine-light

your alternator might be shorted out internally. try taking it out and having it tested. my truck had the same problems. i also had problems with power locks and windows when the battery went dead