* Under the hood, in the under-hood fuse box (power distribution box): This is the most common location. The fuse box is usually located near the battery. Look for a relay that's labeled "ECM" or has a similar designation. The relay itself might be a smaller size than others in the box. Consult your owner's manual or a wiring diagram to be absolutely certain.
* Inside the car, in the passenger compartment fuse panel: This is less common for the ECM relay in a '89 but it's possible depending on the trim level and options. Again, your owner's manual or a wiring diagram will help you locate it.
To find it definitively:
1. Consult your owner's manual: This is your best resource for the specific location.
2. Use a wiring diagram: A wiring diagram for your specific 1989 Mustang will show the relay's location and its connections. These diagrams can be found online through various automotive parts websites or forums dedicated to Mustangs.
3. Look closely at the relays: The relay may not be explicitly marked "ECM". It may have a number or other designation. Comparing the physical size and shape of relays might help, as ECM relays tend to be one of the smaller ones.
Remember to be careful when working with electrical components. Disconnect the negative battery terminal before working on anything in the fuse box.
