1994 blue dodge caravan, help

augh! had this van for just over a week, and already sunk 400 dollars into it. it is a 3.0 motor and has 123k on it. bot it from a lady, but test drove for 2 days before purchase. ran extremely well. this will probably sound familiar, but while driving at any speed, the whole thing will shut down, anywhere, anytime. took to mechanic and no codes to read but 12 and 55. he thinks the problem is in the ignition, because not all the lights on the dash will come on any time the van is turned on. the thing ive noticed is that the trans relay little black cube in the relay box by the battery has become hot as a firecracker. not a whole lot to go on, but before i start to shell out lots of cash, could anyone share some advice? ty much.