The relay for the rear fogs should indeed be on the extra panel above This is where it is on my '97 car. You'll note a cutout in the dashboard that allows your hand to rotate when turning the ignition key. The relay you want is on the other side of that cutout. One caveat however, the cars did change a bit during 1997 as well as in 1998.
For the relays, AO member Stixy has posted images of the various forms of fusebox. Try : http://www.alfaowner.com/Forum/3654904-post5.html (Lights not working)
Your description seems to match the second document in that post which is supposed to be for 1998 cars! My '97 car has the fusebox in the first link. Are you sure your car isn't a 1998 'R'? You can look up the date of manufacture by using your VIN number in ePer : FIAT ePER :: The FIAT Forum
As to testing the relay itself. Looking at the wiring diagram, pin 6 ( orange ) should have 12v when the ignition is on. Pin 4 ( black ) is ground. Pin 9 ( Grey/Red ) is from the rear fog switch. Pin 8 is the output to the lights and pin 5 ( grey ) is the output to the warning light. Pin 1 ( brown ) is from main/dip beam and pin 3 ( green ) is from the front fogs. The pins are numbered as you can see in my photograph and match the numbering in the workshop manual wiring diagramme.
With that in mind and the 'rules' from the owners manual :
With 12v on pin 6, pin 4 to negative and either or both pins 1 and/or 3 at 12v then a brief touch of 12v on pin 9 should
energise the relay. It is a brief touch as the rear fog switch is a momentary contact device ( this is how it prevents persistence through an ignition off phase ) and it is the relay that latches ( this is another difference to normal relays ).
I've not been able to confirm this as I have needed to keep my car ready for use this week and was only able to remove the relay briefly to take the earlier photograph. If I can test the theory at some point I will.
You can test the car's wiring as follows ( assuming your car's wiring is the same as mine
Remove the relay.
Pin 4 ( black ) should be battery negative ( ground )
Pin 6 ( orange ) should be +12v with the ignition on.
Pin 1 ( brown ) should be +12v when the car's main or dip beam is on ( check main beam warning light )
Pin 3 ( green ) should be +12v when the front fogs are on ( check the warning light )
Again, with the relay unplugged, if you bridge pin 6 ( orange ) and pin 8 ( grey/white ) with the ignition on the rear fogs should illuminate. If you bridge pin 5 ( grey ) with pin 6 ( orange ) with the ignition on the warning light should illuminate.
It's worth downloading the workshop manual. You're looking for Volume 3 part 2 section 55-7 and there are separate sections depending on your car's year of manufacture.
Hope that helps.