* Under the hood in the fuse box: This is the most common location. The fuse box is typically located near the battery. The relay itself might be labeled, or you may need to consult your owner's manual or a wiring diagram to identify it.
* Inside the cab, under the dash: Less common, but possible on some models. This would require removing some panels under the dashboard to access the relays.
To find it:
1. Consult your owner's manual: This is the best first step. It should have a diagram showing the fuse box layout and identify the wiper relay.
2. Check the under-hood fuse box: Carefully examine all the relays in the fuse box. Many have diagrams on their covers, some are labeled, and some will have visible markings related to the function of the relay.
3. Use a wiring diagram: If you can't locate it visually, a wiring diagram specific to your 1990 F-150's year, model, and trim level will be essential. You can often find these online through forums dedicated to classic Ford trucks, or by purchasing a repair manual.
4. Trace the wiring: As a last resort, you can try tracing the wiring from the wiper switch back towards the fuse box, following where it connects. This is time-consuming and can be difficult.
Remember to disconnect your battery's negative terminal before working with electrical components to avoid short circuits.
