1978 Chevy Silverado Blower motor runs with key on and ac c

I have a 1978 silverado when the key is tuned on the blower runs constantly.A blue wire on the blower relay has 12 volt even when the switch is on.The purple wire to the blower has power with the key on.the red feed wire for the relay has a battery 12 volt constant.The realay is grounded through the body.I have read this is normal on that year is this true or do i have a bad fan switch.Any help is appreciated. Regards Jim