How to Test Fuel Tank Selector Switch [2 Methods]

If you’re driving a truck or a semi-truck you’re more likely to have two fuel tanks. The fuel in each fuel tank is independently used. Quite a few sedans also have the dual fuel option.

Usually, one tank is located at the front and the other at the back.

The fuel selector switch selects which tank you’ll use for consumption.

A defective switch won’t enable you to switch between your tanks. As a result, you cannot use your fuel efficiently.

So how to test the fuel tank selector switch?

There are 2 ways you can test a fuel selector switch. The 1st method is testing the inertia switch cable. Here you must ensure the proper power supply of the switch. The 2nd method is testing the terminals. Where you check the voltage of the front end and the rear end circuit using an Ohmmeter. 

We’ve elaborated on these methods in this article. So, stick with us till the end.

Now let’s dive in. 

Troubleshooting Fuel Tank Selector Switch 

Defective fuel selector switch shows symptoms. Symptoms of a bad fuel tank selector switch are fuel circulation problems, not Responding during Start, etc.

These are common Ford fuel tank selector valve problems.

There are mainly 2 ways you can troubleshoot the fuel tank selector switch. 

Here’s how-

Method 1 of 2: Troubleshoot the Terminals on the Switch

You’re gonna need an Ohmmeter for this method. 

Here’s our recommendation for the best Ohmmeters in the market. 

Use these recommended Ohmmeters for the best results.

Now, before testing out the fuel tank selector switch you should know the terminal pins. There are 6 terminal pins on the fuel tank selector switch. These are- 

  • Pin-1: unused pin.
  • Pin-2: 789-BR/W
  • Pin-3: 786-R
  • Pin-4: 673-DB/Y
  • Pin-5: 29-Y/W
  • Pin-6: 675-Y/LB

Now what you need to consider is that there are 2 circuits in the switch. One for the rear fuel tank and another for the front fuel tank. You need to test both circuits.

Here’s a step-by-step guide on how you should test the circuits. 

Rear End Tank Circuit

You can check either one first. Here, we’ve mentioned how to check the rear end tank circuit first. But you can choose to go for the frontend circuit first.

Here’s how to test the rear-end circuit. 

Step 1: Apply 12V Power

Firstly, what you need to do is apply power to 2 of the terminals. The terminals are Terminal 789 (BR/W) (+) and Terminal 786 (R) (-).

You need to ensure that 12V power is applied to the terminals. 

Step 2: Test the Terminals Terminals 29 (Y/W) and 675 (Y/LB)

Once you are done applying power, you need to check 2 terminals. You need an Ohmmeter to check the terminals. 

The terminals are Terminal 29 (Y/W) and Terminal 675 (Y/LB). 

Now, we need to observe the circuit. If the switch is good then it’ll show a closed circuit. 

Step 3: Test the Terminals 29 (Y/W) and 673 (DB/Y)

Now you need to check the terminals 29(Y/W) and 673 (DB/Y). 

You’ll need an Ohmmeter to test the terminals. 

After attaching the Ohmmeter to the terminals you need to observe the circuit. If the switch is good then it’ll show an open circuit.

Now let’s move to the frontend tank circuit. 

Frontend Tank Circuit

After you’ve done checking the rear-end circuit you need to move to the front-end circuit. The process is quite similar to the rear-end one. 

But it’s sort of the opposite to it. 

Let’s have a look at how you should test a frontend circuit.

Step 1: Apply 12V Power

Firstly, what you need to do is apply power to 2 of the terminals. The terminals are, Terminal 786 (R) (+) and Terminal 789 (BR/W) (-).

You need to ensure that 12V power is applied to the terminals.

Step 2: Test the Terminals Terminals 29 (Y/W) and 675 (Y/LB)

Once you are done applying power, you need to check 2 terminals. You need an Ohmmeter to check the terminals. 

The terminals are Terminal 29 (Y/W) and Terminal 675 (Y/LB).

Now, we need to observe the circuit. If the switch is good then it will show an open circuit.

Step 3: Test the Terminals 29 (Y/W) and 673 (DB/Y)

Now you need to check the terminals 29(Y/W) and 673 (DB/Y).

You’ll need an Ohmmeter to test the terminals.

After attaching the Ohmmeter to the terminals you need to observe the circuit. If the switch is good then it’ll show a closed circuit.

Method 2 of 2: Troubleshoot the Inertia Switch Cable

First, take a look at the fuel tank selector switch wiring diagram. According to it, the power goes from the fuse box to the inertia switch. Then it travels to the fuel selector switch. It goes through an inertia switch cable. And then to the pumps.

An inadequate power supply to any selector wire will disable the inertia switch.

So for the inertia switch to work the selector switch must have a proper power supply.

Here’s how to ensure the power supply to the selector switch-

Step 1: Take Out the Selector Switch

First, you need to pull out the selector switch from the dash. You can try prying the dashboard compartments around the switch using a screwdriver. Then you can just pull the switch right out.

The switch will be attached to a few wires in different terminals. 

Step 2: Check the Power

In this step, you need to check the power of every terminal.

Nominally the power should be 12V in each terminal.

If every terminal has 12V power then the switch has no issue. If not then you need to supply power to the switch. You need to jump the terminals. 

Step 3: Jumper the Terminals

In case there is a lack of power supply you need to jump the terminals. For that, you need a jumper wire.

Attach the one end of the jumper wire to the positive terminal. And another end to the negative terminal.

Then put the car on ignition. This should supply sufficient power to the switch.

FAQs

When should I replace my fuel tanks?

Metal fuel tanks should last for about 10 years. Unless it gets damaged it can last a decade without any problem. 

Are there two fuel pumps in dual fuel tanks?

Yes, there are 2 fuel pumps in dual fuel tanks. There are 2 ways the pumps can be designed in your vehicle. Either in series design or parallel design. 

What is the average cost of fuel tank replacement? 

Replacement of a gasoline tank costs around $1,261 to $1,410 on average. The cost of labor is projected to be between $254 to $321. And parts cost between $1,007 to $1,090.

Wrap Up

Hopefully, by now you know how to test a fuel tank selector switch. 

A bonus tip for you is to replace the selector switch if it malfunctions. 

That’ll be all from our end. Take care.

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