70 EC w/AC: Hi-Blower draws down dash lighting??

Not a big problem...yet, but I can see that when I run the fan on high (now that the weathers cooling and I need to run some heat), the dash lights dim and, not sure, but maybe all exterior lighting as well.
It's all original wiring w/replacement of old ext reg. 63 amp 10DN to a 100 amp CS130 (PepBoys). Battery is about 6 mo's old and elec./start system exhibits no abnormalities other than also a very minor dimming of dash panel when I hit the brakes or hit the turn signals, but it seems to brighten back up when the alternator senses the load.
Seems like I hear a laborius whine coming from the blower motor (or squirrel cage brg's?) that is louder at low speeds than at full hi, so my first suspicion
is for the worst: access and replace the blower motor. Or, should I try the blower relay on the firewall next to the AC box under the hood? (I think that's it anyway.)
Or, if it is the squirrel cage brg's creating undue drag on the motor, would it be easiest to replace the cage first and see if that eases the draw on the system?
Seems like it wouldn't be a big problem if I never want to run the fan on high, but since thats not an option, I guess that other than at high rpm's, I may be working the life out of the battery.
Comments and suggestions greatly appreciated as I would expect this is a great time of year to discover those exquisite little inconveniences like a murdered battery or melted conductors, etc.