heater blower stays on after shutting van off

hello and thanks if any reply. 2002 chev express work truck 3500 series. ive been reading the fourms on this subject. and am lost now from too much reading. i think what i'm unstanding here is if the blower keeps running with keys out of ignition.its the fan relay which is located under the hood section.and if its your blower settings low med high then its the resistor under your dash inside the truck.am i right here? or is every car/truck different.my blower is draining my battery stuck on high.i had to boost the van this am and as soon as i hooked up the cables to the batteries the blower came on high speed with no key in the ignition yet i drove into town shut van off blower kept running on high speed killed my battery again.while i was driving i switched knob to each setting with no change stuck in high speed.so which relay do i need to change and where is it located in my van.trying to find part number so i can get a new one ty once again

The high speed relay that is built into the blower resistor is stuck in the "on" position- follow the purple (and also the black wire) wire back from the blower motor- it originates at the module you need to replace- it is mounted in the HVAC case-underhood- driver's side- two or 3 screws to remove it- should be about $30-$40 at Autozone etc...

Napa part number is ECHBR79 for $31.