Sorry about that I have a 2000 model 4 door blazer 4x4 LT and the blower shuts off when I switch it onto #4
Thanks

 

The wiring diagram states that it is on the firewall. It should be the only relay on the firewall above/near the distributor.

I can't remember exactly, but is 4 the highest setting?

 

Yes 4 is the highest setting
there is one relay that sits on top of the black box that the fan is housed in that is infront of the passenger footwell area