89 420 sel with 195k

Engine will heat up at idle (stop light and/or traffic) and typically gets to around 90+ but goes back down upon movement. I let it run in the drive and it went to 120 and I shut it down. Checked the fuse box and found the #1 fuse blown. Replaced and ran again - same thing - temp. ran to 120 and the #1 fuse was blown. AC has been running recently - it was checked earlier this spring with regards to refrigerant and it was fine.

I don't have a diagram for the fuse box and only found specific references to fuses based on circumstances in the forum. Does this relate to the auxiliary fan? I found several posts relating to checking this but am not sure that it's related.

The thermostat is about 2 years old. Recently removed the radiator to replace the timing chain/ rails/etc. so the system was flushed and filled with mb coolant (50/50 mix).

Any help would be appreciated.