View Full Version : Blower motor runs after engine is off and gen light stays on ?

75 Coupe
12-31-09, 04:10 AM
Hey Guyz,
My 75 is giving me the business.
After I turn off the key, the blower motor runs, which drained and killed my battery and the generator light is slightly lit and this is with the key off.
I replaced the battery and unplugged my blower motor yet the generator light is still lit after turning off the engine draining my new battery.
I am pulling the cable every time I park now.
( When the blower motor was plugged in and I switched from cold to hot on the thermostat wheel leaving the slide control in the off position the generator light would go from dim to brighter ? )

I have read some similar problems in other threads that seemed to point to a alternator ?

Anyone experience something like this ?

12-31-09, 08:54 AM
It's possible you have bad diodes in the alternator, which allows feedback from the battery through the alternator and back to whatever ground is available. It would be your negative section of your rectifier bridge, in case you want to venture into the inside of your alternator.
If you don't, disconnect the sensor line, the 2 prong plug from the alternator and put a test light or a volt meter between the connection and lead. If your diodes are bad the light or the meter will read.
There is another possiblity. Your blower motor is almost directly wired to the battery and runs constantly when the ignition switch is on. There are generally 2 points the current could jump through to ground. Under the dash there is a relay, which may be fused in the closed position. Locate the relay, pull it out of the board it is plugged into and if the motor shuts off you've found your problem. The other place your leak could be is at the board itself. The heat generated at the relay often melts the board and the connections will touch one anotherand cause a short to ground ( your blower motor ).

75 Coupe
12-31-09, 02:16 PM
Thank you for the reply,
Sounds pretty complex for me, but I will give the alternator a shot with removing the plug and see where that gets me, thanks again and I will post results...

12-31-09, 04:12 PM
I've had the same problem with my 79 Cad. If it is a similar problem, check some of the climate control threads. In my case, it was a melted wiring harness on one of the plugs - I believe where the relay plugs in. The melted harness caused the blower to run all the time, even when the car was off! Happened to me on a trip from MN to FL, luckily it came on within a few hours from home and I drove it in. The relay had failed and went into meltdown. The mechanic replaced the relay, it was under the dash on the left by the parking brake, and fixed the wiring so it was all separated. I'm hardly mechanical but that sounds like my problem from awhile back and could be yours. Good luck! :) Dave

75 Coupe
12-31-09, 06:08 PM
Thank you for the replies, I unplugged the relay under the dash by the parking brake and the lower keeps going, I also unplugged the alternator 2 prong plug and that made the blower motor stop ?
Any suggestions ?

12-31-09, 06:26 PM
The relay by the blower motor might be bad. It has a hot wire running to it at all times.

75 Coupe
01-01-10, 12:32 AM
Found out it was the alternator, voltage regulator, whew !
$49.99 @ Kragen's for a lifetime alternator.

Thanks to all that helped out, I really appreciate all the help...