* Under the hood, in the fuse box: This is the most common location. The fuse box is usually located either near the battery or under the dash (though under the hood is more likely for the relay). Look closely at the relay diagrams on the inside of the fuse box lid. Many relays are unmarked, so careful visual inspection and comparison to a wiring diagram (see below) is necessary.
* Under the dash, in a secondary fuse box: Some S10s had additional fuse/relay boxes under the dash.
To find it definitively:
1. Consult a wiring diagram: A factory service manual or a reliable online wiring diagram for your specific year and engine is your best bet. This will show the relay's location and often its appearance. You can sometimes find these diagrams through online forums dedicated to classic Chevy trucks. Search for "1989 Chevy S10 2.5L wiring diagram"
2. Trace the fuel pump wiring: If you can locate the wire harness leading to the fuel pump (it will be a relatively thick gauge wire), you can carefully trace it back to the relay. This method requires some basic electrical knowledge and is time-consuming.
3. Test relays: If you have a multimeter, you can test the relays in the fuse box to see which one controls the fuel pump circuit. This involves checking for continuity in the correct positions.
Remember to disconnect the negative battery terminal before working with electrical components. Be careful when probing wires.
