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relay switch question

4K views 22 replies 8 participants last post by  teecro 
#1 · (Edited)
Im installing an air horn/pa (whelen).
I bought a stand alone 40 amp relay.
If I wire up the airhorn using the relay will it still
pull electricity when the truck is turned off?
I dont want this thing to drain my battery
Thanks!

Would the stand alone horn switch prevent the battery from draining?
(the horn switch is wired on the hot wire)
 
#3 ·
So if I use the relay it can drain my battery?
Is there some sort of accessory point in the fuse box (under the hood) I can attach the wires to?
 
#6 ·
For some reason I thought the relay drew a small amount of amps even when the button is not pressed..............
 
#9 ·
I can not get this horn/pa to work with the relay.
Maybe I got the switch wire wired up wrong,
I run + & - from battery directly to the unit it works fine.

I dont really need to use a relay, i just wanted to use is it so it would not drain the battery.

IS there an adapter plug that I could use to plug into an accessory port in the
fuse box under the hood? If there is an accessory port does anyone have a pic?

I have not taken any pics and I have not mounted the switch yet.
I think I am going to mount it next to cup holder near the emergency brake.
 
#10 ·
Whether using a relay or not there is no battery drain unless you're pressing the horn button and drawing power.

Clint
 
#12 · (Edited)
First of all I'd suggest that you add at least an add-on fuse block like the one
pictured below ( Amazon... $10 ), you're going to add more circuits, so just
suck it up and prepare for it now.

I'm going to assume you have a standard "Bosch" type relay, (black cube with 4-5
terminals on the bottom). If you look at the terminals, you'll see that the have
numbers in the plastic molding next to them. No's 85 and 86 activate the relay
itself, 85 goes to a ground, 86 goes into the cab to whatever switch turns on your
lights. No's 30 and 87 provide power to your horn, 30 goes to the fuse block
mentioned above or the battery + terminal in what ever other way you choose to
power it, 87 goes to the power terminal of your horn. The ground terminal of your
horn still needs to be grounded. If you have the five terminal relay, just ignore
the center terminal (87a), that's not used in most applications.
 

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#13 ·
I think I am going to go with an Add-A-Circuit.
Thats if I can find the right size locally.
I stopped at OReillys and they had the regular size
one but I need a micro sized Add A Circuit.
Will keep looking I guess.................
 
#17 ·
I wired it up to relay relay exacttly as the diagram showed. Maybe bad relay.
Anyway, I am going with add a circuit. And all the people who stated that
this unit does not draw current when not in use is simply wrong.
It looks like it is 45mA............
 
#19 · (Edited)
I've got a fused 80 amp line coming from the battery dropping into the cab under the driver side dash. From there a 10 amp inline fuse to the momentary switch and then back to + on the airhorn and voilà! No power drain possible... I mean think about it, if you just connected 5 feet of wire to your positive terminal and then just taped off the end do you think your battery is going to die? this is the same thing.

P.S. I believe the airhorn/PA only comes with the PA mic and you need to provide a momentary switch separately for the airhorn.
 

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#20 ·
Nice setup. And of course I have a momentary sw.
I think I am going to mount the unit under passenger seat.
Did you look at the electrical specs that came with your horn.
It lists right there what the draw is when sitting idle.
I understand about the momentary switch but if you look
at wiring diagram the unit is still being fed power thru
the red wire whether that switch is open/closed.
Atleast that is how my diagram shows. Maybe yours
is different if you dont have a microphone.
My diagram calls for the switch to be placed
in the white/brown wire, not the red one.
 
#23 · (Edited)
When you ask vague or incomplete questions don't be surprised when you receive vague and incomplete answers. Now that we have all the facts your answer is easy as 123...

To use a relay in your install...
30 goes straight to the (+) side of the battery or any other source of constant (+) 12VDC HOT.
87 goes to power up your unit, the red (1) wire in the above drawing.
87 also goes to one side of your momentary contact switch and the other to the white/brown wire (3)
86 goes to chassis ground.
85 goes to any switched (KEYED) power source found in your cabin such as radio.
And of course (2) must also be connected to chassis ground...

Key ON unit will be energized and ready for use. Key OFF unit will be de-energized and thus have no draw on your battery.
 
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