dammit, Jase! Does your preamp have switched outlets and can't you plug the fan in one and the amp in another and power it up from the pre or another power source>
Or is the fan part of the amp? I say if so, always leave it switched to turn on with the amp!
Doofus-proof.
If you gotta use an external fan then mark the side of the cord with the wide blade with a marker before filing it down and mate that turkey like porn. No interruptus crap. Leave it there.
Even IIII can't mess that up