I have a 1989 with the 305. I have a problem with something backfeeding into the alternator which makes the alternator "hum" when the car is off. So, my battery just dies if the car is not run on a regular basis. We replaced the alternator with no luck, as soon as you put the plug into the alternator it starts to run. What could be drawing power when the car is off? We unplugged the trunk lock and the hood light, the interior has no lights except the two on the floor and they work. Where do the wires that plug into the alternator go? Could they be shorting?

Also, for some reason my cooling fan only turns on when the car is off. We have replaced the thermostat and both cooling sensors, but the car continues to overheat if left running and not moving.

Has anyone had problems like this? We are at complete losses with both issues. I'm about ready to put a grenade in the gas tank. PLEASE HELP!

 

Brown wire to alternator should only be "hot" in "run".
The brown/white wire on the cooling fan relay should also be hot in run, and the relay should kick in when the green wire is grounded.
Sounds almost like someone has been hacking the wiring..
You can find '85 Camaro wiring diagrams here: http://www.geocities.com/vtcamaro/Wire-Diagrams.html

 

I suspect the alternator has bad diode trio. It's probably easier to just install a rebuilt unit rather than tear down the alternator to replace just the diodes.

Essentially, the battery is trying to make a motor of the alternator.

 

Fullsizewagon might be onto something here.
If you replaced the alternator and you still see the problem, it is very unlikely that the second alternator would have an identical issue.

If you unplug the connector on the alternator, does the humming stop? It should.

Get a voltmeter or testlight and check the brown wire on the alternator plug. It should have 12V only with the key on, no voltage with the key off. If you detect 12V on the brown wire with the key off, you have a problem in the ignition circuit (which would explain why the fan comes on with the key off - the fan and the alternator are controlled by the same fuse).

Another thing: what happens when you pull the FAN fuse under the dash?

Hope this helps.
Lou