Open hood to full position.
Three wire connector on the firewall, behind booster.
Red/Blk/Yl

That is test connector point to blower/regulator:

Key ON , ACC to Defrost.
You want to see 12v across R/Blk...and variable V [ 2-9V.] from Yl to Blk , depending on ACC setting..The R/Blk are 12v feed and the Yl is trigger sig to regulator for speed control. If YES to both test , the problem is downstream from the connector [ meaning down at the blower/regulator.]
If NO , then the prob is upstream from connector [ meaning fuse , ACC panel, etc.] This test point is used b/c it seperates the cabin controls from the engine compartment circuit. [ making diagnosis simple, as it is a circuit mid-point and easy to get to]
Finally, if YES at test, then go to blower and ground the blu wire @ blower with a jumper to ground ..if the blower then starts , the prob is the regulator...if NO , it is the Blower [ brushes, frozen bearings , etc]
That's it.........

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A Dalton