* Under the hood in the fuse/relay box: This is the most common location. The fuse/relay box is usually located near the battery or on the inner fender well. Look for a box containing fuses and relays. The relay itself might be labeled, or you might need to consult a wiring diagram (available online or through a repair manual) to identify it. Look for a relay that's associated with fuel pump, fuel injection, or a similar description.
* Under the dash: Less common, but possible. This would typically be in a fuse box located under the dashboard, often near the steering column. Again, you'll need a wiring diagram to identify the correct relay.
* In the passenger compartment fuse box: Some models had a secondary fuse box in the passenger compartment.
How to find it using the process of elimination (safest method):
1. Consult a wiring diagram: This is the most reliable method. A wiring diagram for your specific year, make, model, and engine will show you exactly where the fuel pump relay is located and how it's wired. You can often find these diagrams online through repair manual websites (often for a fee) or sometimes for free on forums dedicated to classic GMC trucks.
2. Check your owner's manual (if you have it): While it might not pinpoint the exact location of the relay, the owner's manual may show the location of the fuse/relay boxes.
3. Look for similar vehicles' diagrams: If you can't find a specific diagram for your 1988 Suburban 2500, try finding diagrams for similar year GMC trucks or Chevrolet Suburbans. The location might be similar.
4. Visually inspect the relay boxes: Once you've located the fuse/relay boxes, carefully examine each relay. Some relays might have markings indicating their function (though this isn't guaranteed). If you see a relay that looks larger or more substantial than others, that might be a clue.
Important Safety Note: Before working on any electrical components, disconnect the negative terminal of your battery to prevent accidental shorts or shocks.
If you're uncomfortable working with automotive electrical systems, it's best to take your Suburban to a qualified mechanic. Improperly handling relays or fuses can cause damage to your vehicle's electrical system.
