Sounds like something has a Dead Short (+ directly to ground)it may be the armature in you wiper motor. It is very hard to say what exactly as the spades and wires can and may have been moved and changed over the years. I know while I was getting my car ready for inspect, I found none of my fuses were for what the manual or fuse box said they should be.

With that said...

Do you have a multimeter?

Its easy to troubleshoot if you have a meter and know how to use it.

I would determine which side has power going to it, remove the fuse and set to voltage. Check either side.

Once you determine that pull the spades off on the non power side and check for continuity (reduced resistance) to ground on each one.

Trace back the one that has the least Ohms/resist...

If you dont have a meter...

The way to do it without a meter is to have a 12 volt tester light (a 12 volt marker light #1156 & scrap wire.. works with a friend holding one wire to the bottom contact and one to the case), disconnect the fuse. One wire on the tester will go to chassis ground the other will touch the fuse connectors. The one that lights up is the hot or power side. Disconnect the spades on the non power side. put the fuse back in, connect 1 spade at a time and actuate everything untill the fuse pops on the wire that goes to the defective unit/chafed wire etc.

Now trace that wire back to its source looking for chafes cuts, anything that can go to ground. If all is good it may be th item is defective/broken..

good luck, hope this helps. This is common troubleshooting for all cars.. Be glad this is on an old volvo and not a more modern one!
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I have to work on it...... MYSELF?