3-Position Switch Troubleshooting

Switch Basics

If you are experiencing problems and suspect your switch, here is a quick and easy way of testing for proper function. The picture to the right should be used for reference regarding pin layout, as the actual numbers on the switch are difficult to read.

Occasionally these 3-position switches are assembled incorrectly, and the face plate of the switch is assembled upside down, which would make the purge mode (large light) vegetable oil mode, and the vegetable oil mode (small light) the purge mode. This can be remedied by gently prying at the pivot point at either side of the switch. Once the face plate is loose, it can simply be rotated and snapped back into position. The other choice is simply to remember the large light is veggie, and the small light is purge.

The light no longer illuminates on the switch.

The switch draws it's power for the light from the red wire, connected to pin 2. The light utilizes pin 7 as a ground. Using a multimeter, verify you have power coming into pin 2. Next verify you have a good ground on pin 7. If both connections are correct, the internal LED has failed, however the switch will still function as it did previously, with the exception of the light.

My vehicle purges when it is in vegetable oil mode.

Using your multimeter, begin by verifying you have battery voltage on the red wire (terminal 2), and that the valve is properly grounded.

Should the electrical connections be good, and the face plate in correct orientation, remove the switch from the socket and test for continuity between pin 2 and pin 3. Lack of continuity (no reading; open circuit) is a sign the switch has failed.

Test of continuity between pins 2 and 3

My vehicle does not purge, but does run on vegetable oil.

As in the previous diagnostic step, remove the switch from the socket to gain access to the pins. Test for continuity between pin 5 and pin 4.

Testing continuity between pins 4 and 5

My vehicle burns vegetable oil, but fills my diesel tank with vegetable oil.

Begin by verifying battery voltage on pin 5. Next, remove the switch from the socket and test for continuity between terminals between pin 5 and pin 6. Lack of continuity (no reading; open circuit) is a sign the switch has failed.

Testing continuity between pins 5 and 6