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I am servicing a truck rig. This is the system that reads the "turn light switch" and "windscreen wiper switch".

I would like to understand how the image plate 1 reads each position of the levers. On the lever there are 3 contacts that are indicated with blue arrows in image 2. When the lever of image 2 is placed and pressed on the printed circuit board of image 1 it is possible to read each position of the lever.

I wonder how this reading is made since the contacts indicated with the blue arrows are made of a nonconductive material.

I thought it might be a change of capacitance, since capacitance depends on the physical characteristic of the capacitor and so contacts could change that characteristic.

Has anyone seen this kind of position reading system and could opine? Image 1: Printed circuit board.

Image 2: Lever with contacts

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  • \$\begingroup\$ Measure the resistance while changing the lever see if that makes a difference \$\endgroup\$
    – Voltage Spike ♦
    Commented Sep 26, 2019 at 17:33
  • \$\begingroup\$ I think what we're seeing in the first photo is the top layer of a membrane switch. The PCB below it will have separate contact areas for the three positions of the turn indicator. The "fingers" in the strictly mechanical assembly in the second photo are simply pushing the layers of the membrane switch together. \$\endgroup\$
    – Dave Tweed
    Commented Sep 26, 2019 at 18:05
  • \$\begingroup\$ If it’s black contacts then it is a medium resistance carbon polymer to bias CMOS to drive a FET Switch \$\endgroup\$
    – D.A.S.
    Commented Sep 26, 2019 at 20:35
  • \$\begingroup\$ do the rounded knobs in bottom picture extend and retract when you move the lever? \$\endgroup\$
    – jsotola
    Commented Sep 27, 2019 at 0:57

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