First; double-check your fuse layout with the handbook. There are three different makes of fusebox used on these and they also vary year-by-year. Yours should be the 97-99 box in which fuse 21 [10 amp] in the dashboard fusebox is for the A/C - but trust nothing about PSA fuse positions.
If both contacts in the fusebox for that fuse are dead; then find the wire coded KK2 coming from one output of the ignition switch [fusebox plug H - pin 5A] and see if that is live key-on. If not; check the same wire code leaving the ignition switch.
Plug H is one of the multi-plugs, not the diag socket. The feed to fuse 21 is straight from key position 1 of the ign switch vis wire KK2. KK1 is the main ignition switch output on position 2.
This is looking very like a ign switch failure.
If memory serves; there should be 5[6?] wires on a petrol switch? Two are permanently live; [BM 1 + 2] one is the starter; [wire 100?] one is KK1; so you want the other one - which should be live when the key is in position 1 and 2. It's number will only appear downstram of the ign switch plug.
Not sure I'd be up to soldering in a relay (I've only just managed to blag my way this far!). Where might I get my hands on a relay? would I end up just blowing lots of fuses with a double feed on the BM1 line?
Is the ignition switch a big deal to change?
Do I need a mina dealer to do it?
Thanks again for all your help ... I'd never have gotten this far
Any standard 4-pin mini-cube 40amp relay will do. [About a fiver.] Both circuits fed off BM1 anyway. BM2 feeds AA1.
Fitting a new switch isn't hard - just a bit fiddly; a Haynes would be a boon.
Depending on the make of the lock and switch assy; [Neiman?] you might have key-chip issues. Some keys have a detatchable head [tiny, hidden, screw] and you swap them on to the replacement lock's key-blades - some locks need their solid keys' chips re-matching to the immobilizer by a dealer.