windshield wiper motor and arduino digital pin burn

Greetings!

I need help figuring out why the arduino digital pin seem burnt and how to fix the circuit. There is a windshield wiper motor connected to 2 relay shield, and to arduino. The windshield wiper motor provides 2 wires that are always shorted together except once per revolution when they are disconnected (park function). I connected one of those wires to digital GND and the other to digital pin 12 which I set to: pinMode(12, INPUT); digitalWrite(12, HIGH); It worked somewhat but now pin 12 seem burnt. I tried on pin 2 and now it seem burnt too because it is always low.

Thanks for your help.

Are you sure those 2 wires are isolated from the motor circuit? That contact is normally connected to the -ve supply to the motor to interrupt it on cycle completion.

Hi, Welcome to the forum.

Please read the first post in any forum entitled how to use this forum. http://forum.arduino.cc/index.php/topic,148850.0.html then look down to item #7 about how to post your code. It will be formatted in a scrolling window that makes it easier to read.

Also a copy of your circuit diagram, in CAD or a picture of a hand drawn circuit in jpg, png?

Thanks.. Tom... :)

Thank you MarkT! You are correct.

Motor has 5 wires. -ground -high speed -low speed -wireA -wireB

90% of the time wireA is connected to wireB. 10% of the time wireA is disconnected form wireB and connected to ground.

If the motor is reversed wireA will be connected to +12 and that would damage an arduino input.

Hi, What model Arduino are you using?

Can you post a picture of your motor please?

[u]Please a copy of your circuit diagram, in CAD or a picture of a hand drawn circuit in jpg, png?[/u]

Can you, with wire A and B disconnected from the circuit, get your motor running and measure the voltage on wire A and then wire B with respect to gnd? This is to see if they at some stage have 12V potential on them.

Most wiper motors have switching arrangements where in the parked mode, a short is applied to the motor to make it stop abruptly.

Also they are wired for "intermittent operation" so A and B may not be an isolated switch.

Thanks.. Tom.... :)