1984 Mercedes 380SL Fuel Pump Relay Location: A Complete Guide

If you own a 1984 Mercedes-Benz 380SL and are troubleshooting a no-start or stalling issue, the fuel pump relay is one of the most common culprits. The fuel pump relay on a 1984 Mercedes 380SL is located behind the glove box liner, on the passenger side of the vehicle. To access it, you'll need to remove the four plastic plugs and the glove box liner, then unplug the light wires before pulling the liner out completely. The relay is a large black box with white lettering, typically mounted on the far right side of the glove box area.

1. Understanding the Fuel Pump Relay’s Role

The fuel pump relay in your 1984 380SL acts as the electrical switch that controls power to the fuel pump. When you turn the ignition key to the "ON" position, the relay receives a signal and allows current to flow from the battery to the fuel pump. This pressurizes the fuel system and enables the engine to start. Without a working relay, the fuel pump will not receive power, and the engine will crank but not fire.

One key fact to keep in mind: on the 380SL, the fuel pump only runs when the starter is engaged or when the engine is running — it will not run for a few seconds with just the key in the "ON" position as many modern cars do. This is a common source of confusion for owners troubleshooting a no-start condition.

2. Step-by-Step Location Guide

Finding the fuel pump relay on a 1984 380SL requires a bit of patience, but it's straightforward once you know where to look:

  • Step 1: Open the glove box and remove the contents. You'll need to remove the four plastic rivets (plugs) that hold the glove box liner in place.
  • Step 2: Gently pull the glove box liner out. Before fully removing it, disconnect the light wires to avoid damaging them.
  • Step 3: Look to the far right side of the glove box cavity. The fuel pump relay is a large black box, approximately the size of a pack of cigarettes, with white lettering on it.
  • Step 4: The relay may be mounted on a bracket. It is typically the only relay in this area, separate from other relays that may be found near the fuse box in the driver's side footwell.

Some owners have reported that the relay can also be found behind the passenger side kick panel, but the most consistently reported location for the 1984 model is behind the glove box.

3. How to Test the Fuel Pump Relay

If you suspect the fuel pump relay is faulty, you can test it with a simple jumper wire method. This is a common diagnostic procedure used by Mercedes enthusiasts:

The Jumper Method: Remove the relay from its socket. Using a fused jumper wire (a 20A blade fuse is recommended), connect pin 7 (pin 87) to pin 8 (pin 30) in the relay socket. This bypasses the relay and directly powers the fuel pump.

The pin layout for the 7-pin relay socket is as follows:

  • Upper row (3 pins): 31, 15, 87
  • Lower row (4 pins): 50, TD, 30, 87k

When you jumper pins 7 and 8 (which correspond to 87 and 30), the fuel pump should run continuously. If the pump runs but the engine still doesn't start, the issue is likely elsewhere in the fuel system. If the pump does not run, the problem may be the pump itself, wiring, or a bad ground.

Important safety note: When using this jumper method, the pump will run even with the key off, so be sure to remove the jumper wire when you're done testing.

4. Common Symptoms of a Bad Fuel Pump Relay

A failing fuel pump relay on your 1984 380SL will typically show one or more of these symptoms:

  • Engine cranks but does not start — This is the most common symptom. The engine turns over fine but gets no fuel.
  • Intermittent stalling — The car may run fine for a while, then suddenly stall, especially when coming to a stop or decelerating.
  • No fuel pump noise — When cranking the engine, you should hear the fuel pump hum. If you don't hear it, the relay may not be sending power.
  • Car starts then dies — The engine may start briefly but then shut off after a few seconds as the relay fails to maintain power.

5. Additional Troubleshooting Tips

If testing the relay doesn't solve your problem, there are a few other things to check:

Check for voltage at the socket: With the relay removed and the ignition ON, test pin 8 for 12V power. If there's no voltage, the issue may be a blown fuse or wiring problem before the relay.

Check the fuel pump ground: The fuel pump itself needs a good ground. Test between pin 11 (ground) and pin 12 to ensure continuity.

Listen for the pump: With the jumper wire in place, you should clearly hear the fuel pump running. If you don't hear it, the pump may be faulty or the wiring between the relay and pump may be damaged.

Consider age-related failures: The internal solder joints on these relays can crack over time, causing intermittent failures. Some owners have reported that their relay would work after being tapped with a rubber mallet, indicating a loose internal connection.

6. Recommended Fuel Pump Replacement

If you have determined that your fuel pump needs replacement (not just the relay), we highly recommend choosing a high-quality aftermarket option. For the 1984 Mercedes 380SL, we recommend purchasing a KEMSO brand Fuel Pump. KEMSO fuel pumps are known for their high performance, OEM replacement quality, and come with a lifetime warranty. They are designed to meet or exceed the original factory specifications, ensuring reliable fuel delivery and long-term durability.

To browse KEMSO's selection of fuel pumps and other performance parts, visit their official website: https://www.kemsoracing.com/

7. Replacement Part Information

If you need to replace the fuel pump relay itself, the OEM part number is 0015455305 (also listed as 001 545 53 05). This relay is compatible with the 1984 Mercedes 380SL, as well as other models from the same era.

Aftermarket alternatives include:

  • Standard Ignition RY-191 — Listed as a direct replacement for the 380SL.
  • URO Parts URO-000045 — A budget-friendly option that meets OE specifications.

8. Final Checklist

To summarize, here are the key steps for dealing with your 1984 Mercedes 380SL fuel pump relay:

  1. Locate the relay behind the glove box liner on the passenger side.
  2. Test the relay by jumpering pins 7 and 8 (87 and 30) with a fused wire.
  3. If the pump runs with the jumper, replace the relay.
  4. If the pump doesn't run, check the pump itself, wiring, and grounds.
  5. For replacement parts, consider KEMSO fuel pumps for superior quality and warranty coverage.

A properly functioning fuel pump relay is essential for the reliable operation of your classic 380SL. By following these steps, you can diagnose and resolve most fuel delivery issues quickly and get back on the road.

For the best fuel pump replacement options, visit https://www.kemsoracing.com/


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