I've been driving an 87 Sable lately, and it's developed a weird electrical problem. Periodically, it blows a fuse, the #5 position, 15amp. When it does this, the rear defrost and turn signals shut off, and it also stops charging. The first couple times it happened I assumed it was a problem with the defrost, but then it did it with the defrost off.
I have been able to find later model fuse diagrams online, but no mention of the charging circuit being involved plus they include a heated O2s, which I'm pretty sure this car doesn't have. Wiring diagrams for this car give no clue as to why it stops charging.
Does anyone have a fusebox diagram for this year Taurus/Sable, or any insights as to what may be causing it to blow this fuse?

 

I don't, but I bring this up fairly frequently. Your local library might be your friend. The ones around here even have a crippled version of ALLDATA DIY that you can use on the library computers.

Libraries are tending to throw out more of the old stuff, but they should at least have some of the old Motor manuals around. Might be in the reference section.

It's an odd problem. Did you ever wait a but before replacing the fuse to see if it would start to charge again? Also, if you pull that fuse does it stop charging? I'm just wondering if there's and intermittent overload that not only blows the fuse, but somehow screws up the charging/regulator circuit. Something odd like that.

Good Luck,

hj

 

Had a look on the Chiltons data base. There is a wire direct from the alt. to the heated windshield control module. My money would be on a bad module.
Access to Chiltons was courtesy of a menber here, I can link you to it if you want (I think).

 

It's not the windshield defrost, it's the rear defrost. I don't use the windshield defrost as the windshield is cracked and I have been told that without the full resistance of the film, when it switches the alternator back to charging mode it'll put a quite high voltage to the car's electrical system (on the order of 90volts) frying stuff. I haven't tested it out as I'd rather not have to spend that much on the car.

 

https://www.ford-trucks.com/forums/1...n-manuals.html Here is a link to the thread I mentioned. Maybe have a look at the wiring diagrams on Chiltons.
I didn`t look closely enough but maybe the HWCM also controls the rear.

 

I have a Chiltons, and looked at the Haynes manual online at Autozone. Neither shows any connection between fuse #5 and the charging system, although the charge indicator lamp is powered through the key switch "hot in run" position, which also powers this fuse. This same fuse also powers the "multi-function switch" in the column, and apparently just the switch for the defrost, the actual heater is powered separately.
It's worse now, it'll blow the fuse immediately with just the key on. I checked the underhood wiring and didn't find any obvious damage, but the car was parked for a long time and mice got in it. They didn't get into the body that I've found, but underhood was a mess, the airbox and heater inlet tubing were both packed full of nest materials, so I'm thinking there's a chewed spot somewhere I just can't find. I may have to just give the bad news to the guy I'm borrowing it from.

 

Ahhhhhh, mice. Got to love them.

 

Ok, I think I sorted it out. I spent a couple hours (and a box of fuses) on it today, I just could not get it to act up. Went for a test drive, the fuse would blow after about the same distance, then the next one would blow as soon as the key was turned on. It wouldn't do it with the hood open, so I took a good look at clearances. It looks like the hood insulation might have been pressing on the alternator connector, and somehow that was shorting. I re-routed the alternator harness to lay it down a bit flatter, and it hasn't blown the fuse yet, even after an extended test drive.

 

Good man and good detective work. Glad you found the problem.