Since you seemed to be able to measure amps to get 21.... way too much for the normal bath fan of any kind I have ever seen... it sounds like you have a short somewhere in the wiring to draw that much current. The mini wires on the fan normally are not that big even...
And since you tried a 2nd motor
Unhook the motor leads and with the power off, start using an ohm meter to check for continuity to DC ground from the hot side. If you have continuity to ground on the hot wire when you flip the wall switch on, well start back tracking from there to find the short.
Good luck and hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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