I would just pull the relays ,test them on the bench, then check you have 12v + at the live terminal of the relay socket,then jump the switched and live terminals and see if fan spins up
(because you can do that test without the engine being hot and the ecu calling for the fans to be on)
removing the covers may be possible on newer relays , but you run the risk of the covers popping off every time you want to pull the relay
also have you pulled the fuses and checked they are sound with a continuity tester / multi meter ,or are you just looking ,thinking they are ok
Swapped relays K12 and K13 (Hella made in USA) for K12 and 13 from 04 car (made in Spain). Idled engine for 30 minutes, fan never turned; disappointing. Plugged in diagnostic, revved engine to raise coolant temperature, at 102 degrees the fan engaged. Phew!
So it looks like it was a failed relay.
ok, getting somewhere now
I checked the fuse for continuity, it was OK.
I found popping the relay cover tricky. I have removed one, cracking it in the process. As you say, this could make removing this relay again challenging.
If the fan fails again, I could pop this relay in and press the points closed, then the fan should turn. Or, as you suggest, I could simply remove a relay and put power on the output terminal with a simple link from 12v+ to output terminal, i.e. terminals 85 to 87.
I presume the relay that failed was the low temperature low speed one, if so goodness knows at what temperature the high temp full speed one kicks in.