To locate it accurately, you should:
1. Consult your owner's manual: This is the best resource, as it will have a diagram showing the location of all fuses and relays.
2. Look for a relay panel: Look under the dash on the driver's side. There's likely a panel containing several relays and fuses. The blower motor relay will often be labeled, or you can test relays with a multimeter if you have one and can identify the blower motor circuit in your repair manual or online wiring diagrams.
3. Check online forums: Search for "1998 Ford Windstar blower motor relay location" on forums like Ford-trucks.com or similar. Other owners may have posted photos or specific instructions.
Because of the variations reported, visually searching your vehicle is necessary. Remember to disconnect the negative battery terminal before working on any electrical components.