# How to test the voltage of a speed sensor and identify the +ve, ground and signal wires using a DMM?

I am a novice and would like to identify each of the wires going to a speed sensor.

Below is a photo of the connector from the mainboard (left) to the sensor (right):

Is it possible to identify the signal wire from the colours? How can each of the wires be identified using a DMM?

That is, should I "intercept" the wires between the connectors and look to find a steady voltage between two wires?

What about the signal wire, what should I be looking for? Will a DMM be able to identify the signal wire?

This is what the service manual wiring diagram shows:

• What is important is what kind of sensor is used, not how it is connected and what the colors of the wires are. How you think that showing a (vague) picture of "a" connector and "some" wires will help in understanding how the sensor works, which is essential in determining if doing anything with a DMM is usefull, is beyond me. It is like showing a picture of a car-tire and asking what the fuel consumption of that car is. So show the datasheet of the sensor before we close this question. Feb 21, 2017 at 8:59
• Thanks for explaining that, how would you go about identifying a sensor? This is a previous question I posted regarding how to halve the signal frequency:electronics.stackexchange.com/questions/283411/…. I have the components now and need to identify which wire is which.
– Greg
Feb 21, 2017 at 9:14

Normally most of speed sensor have 3 wire 1. Positive wire 2. GND wire 3. Signal wire

Now about your question you can't determine exact voltage level of signal wire using DMM because it's interrupt signal & it's voltage level rise only for some mill seconds.

but you can determine which wire is +ve, -ve & signal using voltage deference between each wire (from main board side).

First of all unplugged connector and from mainboard (left in your picture) determine:

1. Voltage diff between light blue & green wire(if it's 12V this means one wire is +ve)
2. Then voltage diff between light blue & dark blue wire(if it's 12V this means dark blue is +ve)
3. Now using jumper wires connect each pin of mainboard to the sensor board (except middle one as most of time it's signal wire). if you rotate the sensor module (eg. bike tire) & see the some voltage(as it's interrupt signal it's voltage rise only for milli sec) then this means middle one is signal wire.

You can also determine the speed as well using Arduino interrupt and voltage divider (if the signal voltage level higher then 5 volt)

Note: I recommend you use oscilloscope etc to determine the exact voltage of signal.

• If the voltage of the signal cannot be detected, is there a way to identify +ve/-ve apart from +ve/signal? For example could a 12V incandescent light bulb be used to see if it at all lights up when connected to signal/-ve?
– Greg
Feb 21, 2017 at 11:08