I have noticed the automotive Bosh style relays don't have any markings stating +/- but protection diodes are specifit to to the coil relay.

How do I know which is positive and which is neg? I am also using a mini pc 12v 5a relay dpdt and no markings on it either. I believe I have fried my 12vdc power source due to incorrect diode placement.

The diode is a 914 and the black band was toward the (+) of the power source output but I have no idea what (+) is for the pc relay.

I have read much to do with relays but have never come across any mention of polarity of the coil.

This is the relay I am using: http://www.infomeld.com/ebay_pix/RS_PCBRelay.jpg

Any help would be appreciated.

 

I doubt a 914 would fry your power supply, they are only good for 2A peak, 200mA nominal before becoming a fuse. Then again, depending on the supply, it could happen.

Use the resistance mode or diode check of your multimeter across the relay with both polarities, if it has an internal diode, the readings will be different for diode, and "open" for resistance. Otherwise, the major difference in relay coils is DC or AC.

The diode "points" towards the positive terminal, so if an internal diode is found on diode check with the red lead on pin B and the black lead on pin A, Positive should go to pin A in the circuit.

 

I doubt a 914 would fry your power supply, they are only good for 2A peak, 200mA nominal before becoming a fuse. Then again, depending on the supply, it could happen.

Use the resistance mode or diode check of your multimeter across the relay with both polarities, if it has an internal diode, the readings will be different for diode, and "open" for resistance. Otherwise, the major difference in relay coils is DC or AC.

The diode "points" towards the positive terminal, so if an internal diode is found on diode check with the red lead on pin B and the black lead on pin A, Positive should go to pin A in the circuit.

I sure wish I new what you just said...

so if they are diff measurements how do I know which is positive?

 

I got 187ohms both ways on the coil terminals using neg/pos of my multimeter on each terminal.