I have a 69 corvette 350. just purchased in May. previous owner ran the black ground wire from alternator to where the black ground wire from blower motor would go next to wiper motor. blower motor ground wasn"t hook up , just laying there. I removed alternator ground and  attached the blower motor ground to where it should go. Blower motor worked but barely, Just to test blower motor i just tested it grounding it to engine block and motor worked fine. This motor has an Holley sniper EFI installed on it before i bought it. Don"t think this any to do with my issue, but just throwing it out . Its been 40 yrs.since doing the classic car thing, so kinda of new a this. thanks for the patience. Dan

Just run a redundant ground wire from the blower motor to the frame, or engine somewhere.

Thanks for responding.  Appreciate the advice. I was just curious why if I hooked the ground where it was supposed to go the blower motor barely worked and curious why the previous owner would run a black ground where blower ground should have. Thanks 

Can't answer to why folks do what they do, but the wiring diagram shows a black wire running from the blower motor to the starter, AND to the wiper motor connection. The ground wire to the starter, when removed for whatever reason, always seems to get either left loose, or attached to the "+" terminal on the starter solenoid....

Do the wipers work properly?

Thanks, the wipers worked fine when i bought the car. just checked them out to see if they worked. Never had the car out in the rain. I will check ground connection to starter in the morning. It was the ground going to wiper connection that was not connected, just left hanging there. Lots of other little things that will have to take care of this winter. I read that the alternator is grounded by the bracket that its mounted to. I aslo read black ground wire on alternator can be attached to radiator,.  Thanks again. Dan

UH...ground wire from alternator attached to the RADIATOR? That's a new one on me! 😦

Thanks Adams. I went and looked for the blower ground wire that goes to starter and found the end of it wrapped in electrical tape not attached. Put on a connector on the end, Installed on one of the starter bolts, heater works great. The gound wire that someone installed from alternator to where blower ground by wiper switch is removed.  blower works great. almost time to put away for winter. then i can work on car. Thanks again. Dan

Glad ya got it working! Funny thing about that particular ground...it seems that it ALWAYS gets left off, or attached to the wrong place when someone changes the starter, or removes the starter for whatever reason. 9 times out of 10, it gets put onto the "Batt" terminal on the starter because it has such a large eyelet on it, and as soon as the battery is connected, it pops the fuse links down by the starter...or all the smoke comes out of the wires, then they wonder why they have no power to the fuse box anymore! 😏 I have found it best to relocate that ground to one of the bellhousing bolts. That way, it is obviously seen as a ground, and has a specific place to go. Now you know where it goes, and shouldn't have a problem remembering. Anyway, glad you got it fixed. 👍

yes, will move it to bellhousing.  Next up windsheid wipers, only work with car running.  Thanks again, much appreciated

Hi, not to start new thread.  Hooked up ground to bell housing.  Blower motor worked great. Next morning,  battery dead. Any thoughts. Thanks.