Electrical – Fuel Pump Kill Switch

This guide covers how to install a fuel pump kill switch to help deter thieves from stealing your AW11.

Preparation

Before we start cutting any wires we really need to understand the fuel pump’s electrical circuit.

Understanding the Fuel Pump Circuit

Here’s the fuel circuit diagram from the factory service manual (with added colors to emphasize the wires we will be working with):

Note: L is the color code for blue. W-B is the color code for white with a black stripe.

Don’t worry if you can’t make sense of all of this circuit diagram, the only thing that’s really important here is the wires connected directly to the fuel pump itself.

Basically power goes in one side (L) and then comes out the other (W-B), which is grounded to the body. When power runs through this circuit the fuel pump pumps. Pretty simple, right?

Now that we know what we are going to be working with, we want to come up with a plan on how we are going to wire up an anti-theft system to it.

Planning the Anti-Theft System

Here’s a rough diagram of how I planned out my circuit:

As you can see from the diagram, we will be cutting the positive wire (solid blue) between the fuel pump connector and fuel pump. All of our components for this kill switch will then go in between that cut wire.

Why Not Just Use a Simple Switch?

You might be wondering why we need a relay. While you could use just a simple switch on the positive wire between the connector and the fuel pump, most switches are not designed to take these kinds of loads and will break, melt fuses, or even potentially damage something else in the circuit. Because of this, we are using a relay.

How a Relay Works

Don’t worry if relays sound scary and confusing, they are really simple once you understand what they are supposed to do. Basically you can think of them as just a regular switch that’s controlled by power.

Terminals 87 and 30 are disconnected by default, but when you put power across terminals 85 to 86 (which is an electromagnet), they get connected. Disconnect the power across 85 and 86, and the connection between 87 and 30 breaks.

Here’s a simple diagram to show you what that looks like:

Now that we know all of that, we are ready to get our parts and bench test the system.

Parts List

  • Automotive Relay
  • In-Line Fuse Holder
  • 15 Amp Fuse
  • 16 Gauge Wire (any color you want)
  • Crimp Connectors and Quick Disconnects (blue for 16 gauge)
  • Heat Shrink Tubing (1/4″ worked great for me)

Bench Test Video

Steps

  1. Remove the plastic rear console box and center console. They are both held in by several phillips screws that are fairly easy to find.
  2. Locate the fuel pump connector.
  3. Isolate the wires going to the fuel pump (solid blue wire and white wire with a black stripe).
  4. Cut the blue wire a few inches past the connector (so you have some room to work with both ends).
  5. Crimp on the In-Line Fuse to the blue wire (the one still attached to the fuel pump connector).
  6. Build a Y-splitter with quick disconnects.
  7. Connect the Y-splitter to the In-Line Fuse and have the other two ends go to terminal 87 of the relay and the switch you chose.
  8. Connect a wire from the other side of the switch to terminal 85.
  9. Crimp on a connector to the other blue wire (the blue wire still attached to the fuel pump), and attach it to terminal 30 of the relay.
  10. Find a suitable ground wire location and connect it to terminal 86 of the relay.
  11. Tuck your wires away and test that the switch works.
  12. If everything works, hide the switch wherever you want and put the center console and rear console box back on.
  13. Smile knowing that thieves have an extra step to complete before stealing your vehicle.

Pictures

Final Test Video

2 comments

  1. Perfect and super detailed, thank you! Can you help me by letting me know what and where the relays are that directly affect the fuel pump? My 1988 AW11 will run for about 10 minutes and just shut off, no other issues. I am pulling up these 4 fault codes: #’s 12, 25, 26 and 41. I’m addressing #41 by replacing the TPS sensor but the others are leaving me confused. Your help is greatly appreciated!

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