ablackcamaro

Hey guys, this isn't car audio related or f-body related, but I put it here for the electronic relay gurus in here.

My problem: my girlfriend keeps forgetting to shut off the lights in her 96 Nissan Sentra, causing me to give her jumps all the time.

What I want to do is install a relay, that has two trigger inputs, one for the dash lights wire and one for the ignition, which when ONLY the dash wire has +12V, will close the contacts to a circuit that just has a buzzer in it. So, when the lights are on and the key is off, the buzzer will make noise, reminding her to shut off the lights.

My question is, how can I make it so that the buzzer circuit only closes when ONLY the lights wire has power? Is there a special relay that has two seperate low current input pins? I understand how the basic relay works but don't know the difference between the different poles or w/e they use to differentiate different relays.

Thanks for the help and I'm looking forward to some ideas, this problem has my mind stumped and I can't wait to figure it out lol (yep...I'm a nerd everybody!!!)

Happy holidays everyone.

ablackcamaro

OK guys, I got off my lazy bum and did the research and this is what I came up with:

It needs two relays, one is a Single Pole Double Throw, and the other is a Single Pole Single Throw.

The SPDT relay is used, so that when the circuit between the ignition wire and ground is opened (the key is turned off,) it will make condinuity between two ground wires (the +12V wire will be ground, and therefore the output high current wire will be a ground.)

Then, the two low-voltage inputs of the SPST are the +12V from the dash light wire, and the ground input for the relay is the ground given by the ignition relay mentioned above. So I now have a +12V and a ground, exciting the second relay, which will power the buzzer, ONLY when the key is off, and the dash lights are on.

Whew I feel good I think this is gonna work guys, any ideas? I can think of one problem, if the dimmer switch is turned all the way down, it's possible to leave the headlights on and not get the +12V at the input of the second relay, I may just wire that wire to a parking light wire so it's gauranteed to have +12V whenever the lights are on. I think I designed it right, so that with the first relay (for the ignition circuit,) when the ignition is off, it's only connecting a ground to a wire, so the battery won't have a constant power drain on it whenever the ignition key is off.

Anybody see any problems with this setup?

ablackcamaro

I figured it out even more guys... for anybody who ever wants to do the same for another car:

Only one relay is needed--the SPDT relay that sends out the ground when the power to the ignition wire is cut. That will be the ground wire for the buzzer, and the parking light wire will the positive wire for the buzzer--no relay is necessary to control the buzzer as they don't pull more than 1 amp of current.

LS1 RULZ

There are pre-made modules you can buy at most auto parts stores to do this. You can do a search for "headlight buzzer" or "headlight alarm" and other words to that affect and come up with lots of results too. I got one thru JC Whitney to put on my Tahoe when I added fog lights to it.