If you have voltage and the correct signal at the connector next to the brake booster, but your fan is still not working, then it couldn't possibly be your ignition switch. I had a similar problem - the blower would come and go intermittently. I "exposed" it three different times - ugh. I was finally able to reproduce the problem on the test bench. If I tweaked the connectors, it would quit - probably a broken wire internally. $200 for a new blower motor with fans solved my problem.

Good luck!