relay for air horns

[runnin4life]

hi
all i have a set of air horns to put on the old mans car tomorrow or the day after

we have lost the wiring diagram but i know how it was ment to go
only prob is i duno what plugs into what on the relay
wondering if any of you guys could help its a 12v 30a relay
with 4 pins with the numbers
1 with 86
1 with 85
and two with 87

now would the wiring change if the horn is positivly or negitivly switched

because i was going to put a switch in line for the horn so when the swtich is flicked on way the horn button set off the normal horn and swtiched the other way it will set off the air horns

if there is a diffrence in wiring for negative or positivly switched horns
could some one tell me what i should plug into what pin for each aplication

cheers
elliot

[chimpboy]

Your existing horn will either have two wires going to it, or it will have one wire and be grounded to the body. Most likely, it will be two wires.

USUALLY but it really depends on the car, the horn will be negative switched, which means that one wire to the horn will be permanently +12V, while the other wire will be switched -ve. You can confirm this with a multimeter or test light to do what you're describing.

I'll do a workable diagram in a sec, based on there being two wires to the horn.

[wayne74]

you would prob find that it would have a pin with 30 on it instead of two 87 unless it was a change over relay.a change over relay would be better if you wanted both horns on the toggle switch .it would be most likely that the horns are neg (-) switched so if ya get a change onver relay run the 30 to a pos(+) ,86 to the original horn swicth,85 through a toggle switch to an ignition (+),87 to normal horn and 87 a to airhorns both sets of horns will need to be earthed (-),when ya switch the toggle swicth it will turn the relay on or off changing the horns over.

[chimpboy]

Maybe this if you really want to retain the ability to use the old horn...

[chimpboy]

you would prob find that it would have a pin with 30 on it instead of two 87 unless it was a change over relay.a change over relay would be better if you wanted both horns on the toggle switch .it would be most likely that the horns are neg (-) switched so if ya get a change onver relay run the 30 to a pos(+) ,86 to the original horn swicth,85 through a toggle switch to an ignition (+),87 to normal horn and 87 a to airhorns both sets of horns will need to be earthed (-),when ya switch the toggle swicth it will turn the relay on or off changing the horns over.

Hmm yes, if it has 87 and 87a that's better... the only possible problem with this is that the horn works only if the ignition is switched on, rather than all the time which is the normal setup.

[runnin4life]

yep chimpboy thats how i was going to wire it
but im not sure what plugs int owhat tab on the relay
the diffrence between the relay you have drawn and the one i have in my hand is mine has two 87's and your only has one and a 30

so im not sure wats the go with the relay
maybe the relay i have is an overseas thing it has made in italy and the kit is from italy (and the same thing applies to the relay i got in a dual air horn kit i putoether today for my car)

if i decide to scrap the relay that came with it and got a decent one of good quality
i need to look for just a ordianry 30a 12v relay right
cus i just forgot we dont have nay fuse blocks left so we weill have to get a fuse block tomorrow if any thing is open

cheers
elliot

[chimpboy]

Odd that your relay does not have a "30" terminal. If it doesn't, then the two "87"s are probably really an 87 and a 30. They are interchangeable anyway - when you put power across 85 and 86 (the coil), 87 and 30 get connected together. It doesn't really matter which goes to the horn and which goes to the battery.