Quote:
Originally Posted by brandlj
A very strange thing happened to my 86 300sdl yesterday. It has a 6 month old battery and it died yesterday while it was parked in my lot at work. Strange thing too, because it was a beautiful 75 degree sunny day.
I had to manually unlock the doors and the trunk, retrieved my jumper cables and hooked them up to my friend's Ford F150. As I hooked up the jumpers, I noticed my aux fan was turning. Everything in the car was off. When I tried to start the car, it would barely turn over, but the aux fan was turning at high speed. I opened the fusebox and removed fuse number 1 and the aux fan shut off and the car started immediately.
I drove home and started to investigate what could be wrong. I dug out the electrical schematic and started to read. I put the fuse back in fuse number 1 and the fan immediately started to run at high speed. I located the aux fan relay in the fusebox and pulled it and the fan stopped. I plugged it back in and the fan started. I unplugged it again and replaced it with one of the other relays ( the one from the power windows) and the fan stayed off.
I believe that my relayy stuck in the on position ( probably old age) and my aux fan killed the battery.
Luckily I have a large stash of used parts and found another relay and plugged it in the power window relay location, charged up the battery overnight, and all seems well. I will monitor to see if the fan comes on again while the car is off.
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You came very close to the verification it was the relay. Had you removed the one that allowed the fan to stop and inserted the bad one again. If the fan ran it would have verified the relay was bad. You were very close and at the present it does look like a relay fault. If you were to put the old one back in now for just an instant and the fan started it is a positive verification
99 1/2 percent of the time.
This verification process is actually more important if the fan would not come on at all. It basically helps or eliminates the chance of something like terminal corrosion being behind the issue. Also you have no way of knowing used parts or even new are good other than with some form of verification sometimes.
This type of habit is developed over time. I dislike any kind os shotgun approach as well. You may never be able to prove or know what the original actual defect was. You only knew the problem. Although with certain intermittent conditions you might be reduced to doing it.