1. Consult your owner's manual: This is the most reliable source. It will likely have a diagram of the fuse and relay panel showing the location and function of each relay.
2. Use a wiring diagram: A wiring diagram specific to your 1988 Eldorado will definitively show you which relay controls the fuel pump. You can find these diagrams online through parts websites or dedicated automotive repair resources (often subscription-based).
3. Visual Inspection (less reliable): Carefully examine the underhood fuse block. Many relays are the same size and shape, making identification difficult without a diagram. Look for a relay that seems to be related to fuel system components (often labeled or color-coded, though not guaranteed). You might try lightly tapping or wiggling relays while having someone check for a fuel pump sound (don't keep the key in the "on" position too long without cranking to avoid draining the battery). This method is risky and should only be attempted with a good understanding of automotive electrical systems.
Important Safety Note: Always disconnect the negative battery cable before working on the electrical system to prevent accidental shorts and injury.
