* Under the hood in the power distribution box (fuse box): This is the most common location. The power distribution box is usually located near the battery. You'll need to consult your owner's manual or a wiring diagram specifically for your truck's year and model to identify the correct relay. The relay itself may be labeled, or you might need to trace wires to confirm.
* Inside the cab: Less common, but some models might have relays located inside the cab, often near the fuse panel under the dashboard.
* On the fender well: Less common, but possible in some configurations.
To find it, you'll need:
1. Your owner's manual: This is the best starting point. It should have a diagram of the fuse and relay panel locations.
2. A wiring diagram: If the owner's manual doesn't help, a wiring diagram specific to your 1990 Ford F350 turbo diesel is essential. You can often find these online through Ford forums or parts websites. They'll show you the relay's location and what it looks like.
3. A multimeter (optional): This can help you trace wires to confirm you've found the correct relay.
Important Note: Working on electrical systems requires caution. Always disconnect the negative battery terminal before working on relays or fuses to avoid electrical shocks or short circuits.
