my radiator fan on an '81 rabbit pickup (gas) keeps running after the engine has stopped and the key has been removed from the ignition---I suspect the radiator fan switch at the radiator, but am open to other possibilities (?)
I thought they did run if they were still hot with the key out. I have an electric fan on one of my vechicles and it does that all the time. It should only cycle a couple of times at most doing that. How hot is the engine when you turn it off? Long run uphill to the house at the end of a sit and go in traffic? Could be time for a new switch but as long as it turns off quickly I wouldn't fret it.
The radiator fan circuit in the early Diesels rely on the radiator Fan switch as the primary switch.
On a/c equipped cars there is a high and low speed operation depending on the temp as the a/c has a 2 speed fan. so your suspects are both high and low relays and or the fan switch.
The fan can run up to 15 minutes after key off which is normal, The fan can also run on with key out if the sun bakes the radiator and achieves 95C on the core.
So if your fan runs for longer than that then I would suspect 1 of 2 things.
Radiator fan relay bad, or the radiator fan switch.
If your fan runs a bit then shuts off that is normal...
If you have been driving for a while and park it, it isn't unusual for the fan turn on when you stop as the radiator temp spikes as the flow is stopped and there is no air movement over the radiator core. (Normal).
Over 15 minutes of running isn't normal after key off.
the radiator fan never stops---I've seen everything you describe when operation is normal, but the fan runs even when the engine is cold and I've had to disconnect it---I switched the horn relay for the fan relay (one only) and no change---when it first got stuck on "on" the 30 amp fuse for the fan melted (the plastic), but didn't disconnect (break)---I replaced the fuse and as soon as I reconnected the fan plug (disconnected to turn it off) the fan started on a cold engine with no key in the ignition---anything but normal
Fuses that aren't reseated occasionally they get corrosion build up on the contacts for the fuse and tend to overheat and melt the fuse panel. I had had that happen on my Cabriolet as I forgot to reseat the fuse for the a/c as it was at the top of the fuse panel.
I usually try to reseat them all every 2-3 years...as it isn't fun playing with the fuse panel on a Cabriolet, just about as bad on a westy.