diode protection

I am trying to use some diode protected micro relays for auxilary circuits in my car.  (Don't ask why they have diodes - they just have !!!)

For my spot lights to work only with main beam, the coil energisation has to be derived from a dim dip circuit.  On the back of the head light there are three wires.  Two of which remain at 12v all the time the any haedlights are on (dip or main).  The third one is at 12v on dip beam and 0v on main beam.

I'm using one of the permanently 12v wires and the one that drops to 0v on main beam to provide the spot light relay coil energistion.  (Working on the theory that on dip, both are at 12v, therefore no current flows and on main, one drops to 0v, so current flows).

I'm assuming that it matters which way round the coil cicuit is connected due to the diode.  If it's the wrong way round, the diode will allow current to flow bypassing the coil and creating a short ??

I've just tried the above and keep blowing the fuse that is in the coil circuit.  But have temp wired a "normal" relay in place of the diode micro and it works as expected.

Will it affect the circuit if I also put a LED illuminated switch in the coil circuit ?

Any suggestions ?

Many thanks ......... Nick.

The Diode just stops current from going back into the circuit when the coil field colapses after power is dropped out. It is connected in reverse bias or opposite of a normal operating Diode in a power Supply. This stops the spike caused from the induced voltage that is generated from the coil.

You should not have a problem adding an LED indicator to the circuit.

Thanks for the reply.

The circuit is now wired up and working, including the LED indication.  After a bit of research I now know fully understand why diodes are used in relays. (As well as lot of other stuff I didn't know )