* Under the hood in the fuse box: This is the most common location. The fuse box is typically located near the battery, often under a cover. Check the diagram on the inside of the fuse box cover. The relay may be labeled, or you may need to consult a wiring diagram specific to your vehicle's year and model to identify it.
* Under the dash: Less common, but possible. Check the fuse panel under the dash. Again, a wiring diagram would be crucial for identification.
To find it, you should:
1. Consult your owner's manual: This is the best starting point. It should have a diagram of the fuse and relay box locations and descriptions.
2. Look for a wiring diagram: A wiring diagram specific to your 1991 GMC Sonoma 4.3L will show the relay's location and circuit. You can find these online through repair manuals (like Haynes or Chilton) or automotive parts websites.
3. Use a multimeter: If you can't find it visually, use a multimeter to trace the fuel pump circuit. This requires some electrical knowledge and is more involved.
Without a specific diagram for your truck, it's impossible to give a precise location. Checking the fuse box under the hood is your best first step. Remember to disconnect the negative battery terminal before working with any electrical components.
