Major voltage drop with blower on?!?

[HOrnbrod]

Did have this problem (major voltage drop) on the 89 (now 99). In the 89, it centered on the ignition switch. Even after going through the entire harness and upgrading grounds, replacing power leads from the battery the ignition switch is apparently the weak link in the dash electronics harness, as almost all of the voltage for the dash moves through the switch. In some cases I have even seen the plugs and/or switch partially melted together due to the resistance. After the upgrade to the 99 dash and electronics I noticed the draw was still major when the blower is switched on - after some research found the age of the blower motor and resistor seemed to have a lot to do with it. Replaced the blower - and the excessive draw stopped.

 

Aged windings...weak magnets...you want to weigh in here Don?

 

Jake, I think excessive amp draw on the blower motor (or any motor) is mostly caused by dry bearings and worn out brushes, especially on startup. It's easy enough to test using a multimeter in series using the 10A AMPS jack. I've never replaced the brushes in the blower motor, don't even know if you can, but have lubed the bearings with a drop or two of sewing machine oil and it knocks the startup amp draw down 25%-50%. This especially applies to starter motors too, especially worn brushes.