As Martin and Austin have said, the power connections are the most common problem.
Every 928 owner needs a test light. The best type looks like an old-fashioned ice pick with a clear handle and an attached wire. The handle contains a 12-volt light bulb, and the wire ends in an alligator clip. In use, you attach the alligator clip to a known-good chassis ground, and touch the sharp tip of the tester to the suspect connection. If you have power, the bulb lights up.
Check both fuses. Look closely at the end of the fuse, and you will see two little metal dots. One dot is power in, the other power out. You should have power on both dots of both fuses. If not, check the medium-sized red wires on the battery positive terminal. It is a good idea to disconnect the battery ground strap from the body, then carefully clean every connection on the battery.
If you are certain that you have power thru the fuses, you can test the fan final power stages. This is the finned black box on the panel in front of the radiator. If you are good with a soldering iron, you can probably fix a faulty unit, but it might be better to check the 928 vendors for a rebuilt unit.
It is a really good thing that you are trying to do your own repairs, maintenance and upgrades. We will be here to help. If you want help, give complete info on your car, including model year, USA or RoW, five-speed or auto, etc. Give a complete description of the problem - the more detail, the better. And, it would be nice to know who you are, but that isn't required...
