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I have a drain on my battery that will run it dead in less than a day. I noticed two of my fuses have a potential across them and I would like to track down where they are supposed to go in an effort to find how the battery is discharging. Can someone point me to a schematic/wiring diagram for a 1981 528i? Or tell me what manual I can buy to get one? Thank you.

A fuse should be a short with no voltage potential across it.

Thanks and apologies for not being clear.

The potential (volt reading) grows when the fuse is removed. I am inferring that if the fuses were in place that a current would be running through them. I am puzzled by why the potential grows with time, rather than being a full 11 V (which is what it rises to).

I am thinking that if I can know what wires these fuses go to from a wiring diagram that I can sort out where the leak is located.

It's still not very clear where you are measuring the voltage and which fuse you are removing...

The Haynes manual is pretty good and has wiring diagrams. I could swear I scanned it years ago but I can't find all of it, I'll try to get it tomorrow night.

Yes, I follow what you're saying and it makes sense, but I test it by measuring current draw with the fuse removed. Most cheap meters will still do 10A these days and even if it's only 200ma it's still plenty. Pull the fuse and put the meter in series.

The fuse in question is in the second row of fuses (starting at the front), it is the fourth one in (starting at the fender side).

It is labelled:

16A Turn signal gauge, windshield wiper washer system, horn relay (headl cleaner system, el mirror)

(the one next to it is labelled: Stop light (radio)

There are two things. 1. There is a current through it. and 2, it is opposite polarity to the other fuses. in other words the small tab is positive and the small tabs on the other fuses are negative.

I have taken a picture but need to figure out how that could be posted or otherwise made available.

Let me keep looking to see what I can sort out. I will post more information when I have it.

A little more information. I noticed the current draw was not affected when the plug to the key switch was disconnected, but disappears when the hazards are turned on OR if I disconnect the hazard switch.

Question: Could it be the switch itself, or should I be looking further down the line?

I would suspect the hazard switch.

Either disassemble it (scour the FAQ) and sort out the electrical paths inside, or easier, swap a known good switch. Check the wiring from the switch, there are many connections.

The Germans were good at continuing an electrical path from a device to power another to reduce wiring thereby making troubleshooting more difficult. A good wiring diagram is essential.

I pulled the switch yesterday and the battery did not drain overnight. I then pulled the switch apart, but couldn't figure out what could be wrong with it, so I reassembled and reconnected (to see if it still worked). It did, but I don't see the signs of the draining current on the fuse box. I will leave it connected tonight and then see if it drains the battery. I have a replacement on order as well.