1. Consult your owner's manual: This is the most reliable source. It should have a diagram showing the location of all relays and fuses.
2. Check the underhood fuse box: Open the hood and locate the main fuse box (often near the battery). The cover should have a diagram showing what each fuse and relay controls. Look for one labeled "fuel pump," "EFI," or a similar designation.
3. Look for a smaller fuse/relay box: Some models had a secondary box, often located near the battery or under the dash. Check for this as well.
4. Use a wiring diagram: If you can't find it in the fuse boxes, a wiring diagram specific to your 1990 Pontiac Sunbird's engine and trim level (e.g., 2.0L, 2.5L, etc.) will show you the relay's location and circuit. You can often find these online through automotive repair websites or forums.
Without knowing the specific engine and trim level of your Sunbird, providing a precise location is impossible. Always remember to disconnect the negative battery cable before working with electrical components.
