Electrical Wiring Assistance
 

Hey guys. If there are any EEs in the room, I would greatly appreciate some help. Let's get this out of the way first: Yes, I'm adding some train horns to this car. I did them on my old Outback as a fun project, and they were so hilarious that I want to add them again to this car.

Now, on to the question. What I'm trying to do THIS time around is not just throw tons of wires and relays at it until it works. I've been brainstorming ways to do the wiring the way I want, using this free online tool to draw some diagrams. I've come up with ALMOST what I want, but I have some outstanding questions. Please refer to the attached diagram.

What I am trying to do is INSERT some wiring without modifying the stock wiring at all. Basically, all I'm doing is adding a relay between the stock relay and the stock horns, so that I can use an additional switch in the dash to select between stock or train horns. The questions I have are:

1. I think what I want is an SPDT relay. My question is that this diagram tool showed me that there are Polar/Polar-Diode/Non-Polar relay types. I'm not really sure what the differences are, but I *think* the non-polar type only requires a current to flip the switch (switch flips based on which way the current flows), which is what I would want, as opposed to a polar relay, which requires a constant current to remain flipped to the alternate output, which is NOT what I want.

2. If what I've said above is correct, then I'm not sure what kind of switch I need. I think what I want is a two-position momentary switch, which would allow me to send the +12V from the cigarette lighter in either one direction or the other through that relay, but I'm not sure how that would work from a current perspective, because I need two grounds, and I'm unfamiliar with relays so I'm not sure how the wiring would work between my added switch and my added relay.

Can someone clear up that part of my design for me? Would GREATLY appreciate the help!

Bump! Surely someone here knows the answer to this!

I'm a freshman EE major, and right now I don't really have the time to figure it out all right now (more like I'm too lazy to:D But hey, that's true with nearly all engineers. It's usually the defining characteristic that makes us do what engineers do.)

If you have the time, patience, and knack for these kinds of things, then why don't you set up your own circuit using a bread board, maybe using 2 different buzzers in place of the stock and modified horn. Test it out. Have fun.:party0030:

Not E/E.

I have been told however, that a compressor type horn will require heavier gauge wiring for that circuit and added relay.
Probably directly from the battery rather than anywhere on the existing loom.

Caveat, I'm an EE but my field is semiconductors and it's been a loooooooooong time since I had to look at relays.

You polar terminology confused me. Normally relays are referred to as NC (normally closed) or NO (normally open). As drawn, the stock setup is normally open and when you energize the relay it closes.

I think the simplest solution would be add the new horn using the same type of circuit as the stock one. Then just have your selector switch choose to energize one or the other relays.

EDIT: I'm assuming here that the 12V supply you connect can sufficiently feed the new horn.

This^

Heh. I'm an aerospace engineering major, so I know all about that :P

I was considering building a practice circuit, but I figured I'd ask first before I start wasting money on parts unnecessarily, lol.

It isn't compressor DRIVEN in that sense. These horns require a dedicated, pressurized air supply. There will be a Viair compressor charging a 2 gallon air tank, but that will be a separate wiring setup, and yes, that will use heavy-gauge wire running straight from the battery. To activate the horns, I just need to trigger a solenoid valve.

I guess I should have better described my end goal:

The stock system uses a relay to trigger a direct-from-the-battery +12v feed to the horns (as drawn in my diagram, all the +12V sources start at the battery in some form.)

What I want to do is be able to redirect that 12v to either the stock horns, or the solenoid valve that opens the air line. To do that, I don't want to use a MOMENTARY relay. I want a relay that only requires a momentary current to FLIP it and then it will STAY in that position. That way I don't need a permanent 12V feed to the relay. It will either be permanently set to route to the stock horns, or permanently set to route to the solenoid.

I'm pretty sure that makes sense, I just don't know what the terminology is. What you say makes sense with NC vs NO (the polar stuff confused me too), but I think what I'm looking for is a relay that is NC in either one state or the other. So it's either closed one way, or close the other, but never open.

I think the circuit I described does what you want.

Think of it this way. Your air horn is the same circuit as the existing horn. What you want to be able to do is select which horn to use. The simplest way to do that is just switch between the two circuits. You don't need a momentary switch to do this, you just need to select one of the two circuits.

Ah, I see what you were saying. That is the setup I had originally, but what I am trying to do in this case is simplify the wiring and parts. If I can use the stock relay for BOTH horns, by simply redirecting current, I think it might make more sense than building a completely separate circuit for the second horns.

The nice part about doing the separate horn circuit is that you don't mess up the original one.

Also, wiring in the selector switch should be a lot simpler and it doesn't require power to work.

I see what you want there and it's a pretty good idea. Although it would be more efficient to do it with op amps to make a flip-flop, you can also make a latching circuit with a double-ganged NO relay.

The second gang runs in parallel with your momentary switch so it keeps the relay energized when closed. The only way to release the latching circuit is to remove power.

Got that covered then.
Just needs a rocker switch where there isn't a snow button on the manuals.
Might consider an irreverent graphic icon for it.

http://markewbie.weebly.com/uploads/...550817.jpg?357

Got the info from motorcycling sites, so not quite as sorted for tank space.
Though one guy mounted a triple horn through his windjammer and actually did mount a tank.

First off, I want to thank everyone for their replies so far. I've been Googling some of the terms you guys use, but bear in mind that I know NOTHING of electronics other than what I've managed to cobble together with relays from RadioShack, so almost all of that terminology is stuff I have to look up before I even begin to understand you, lol.

As far as running in parallel, I don't want any part of the circuit to have to remain continuously powered. I want the relay to remember the last position, even when the car is completely powered off. The cigarette lighter only receives power when the ignition is on. I could wire it to a constant +12V source, but I don't want any battery drain at all when the car is off. However, I DO want it to remember which state it is in because I want the chirp I use with the remote when I lock the car to be able to come from either horn set, as it would be an easy way to show friends without having to get into the car, start it, press a toggle switch to "activate" the alternate relay, and then tap the horn.

Do you know if the chirp circuit is wired in after the steering wheel horn switch? If you want to retain that function it will probably change the circuit you need.