Graham;

Refer to wiring diagram at: http://www.sw-em.com/122S%20Wiring%20Diagram.jpg

Blowing Fuse1 is quite unusual and likely caused by a direct short on the circuit supplied by this fuse...Hint: Remember all work or unusual conditions leading up to problem (and start troubleshooting there).

Fuse 1 supplies Wipers, Fuel Gauge, Blower, Blinker, OIL Indicator, AMP Indicator...has anything been changed on those loads or that circuit recently?...was anything done to wiring under dashboard?...has anyone done any "wiring" or otherwise mucked around (sounds like they got it wrong!)?

Troubleshooting suggestion: Remove (blown) Fuse1 from Fuse Block and connect a spare brakelight bulb (or 12V test lamp) to its terminals. This will help in locating the short safely and without wasting fuses. Bulb will be ON when IGNition is ON, for as long as short is present (since short completes circuit to chassis)...start by unconnecting supplied loads one at a time (if you honestly can't think of nothing which was recently touched...if you can...then start there and double check what was done)...when repair/correction has been made, replace lamp with fuse...

Please report findings, Good Hunting!