Horn Relay

[DarrenSV650S]

What sort of relay do I need for my new LOUD horn

[yorkie_chris]

Stebel supply a 30A universal one, plenty big enough.

[the_lone_wolf]

if you don't get one with the horn you buy then maplins do a 40A 12V one for automotive use for a few quid

What both of the posts above are trying to tell you is a 12v Bosch style automotive relay. Make sure it's 12v, and not 24v!

These come in either SPDT or SPST versions. How are you doing your wiring? I'm betting that you'll want to use the SPNO pins, so if you get an SPST, make sure it has SPNO, otherwise just plump for SPDT to be safe.

Confused?

SPDT have 5 pins, SPST have 3 or 4 (depending on type). Bosch type relays have a common layout, and all pins are numbered.

The 'coil' used to activate the relay will be labelled as pins 85 & 86. Your horn switch wants to be wired through here.

The SPNO pin is labelled 87, and the "common" is labelled 30. If you have 87a, ignore it, as that's SPNC. Wire up to SPNC, and your horn will sound whenever you're not pressing the button, and stop when you do press it. Comical error, but a school boy one.

OK, so, horn button is wired through the coil (85 & 86), next, wire from battery positive to SPNO (87) and then from common (30) to the new horn. From the other side of the new horn to ground somewhere (bike frame, battery negative, take your pick).

Ignition on & sh*t yourself at just how loud it is.

You stopped reading this post a long while ago, didn't you? Yup, I'm bored in work - 8am on Sunday - should be a law against it...

[the_lone_wolf]

Originally Posted by Baph

Yup, I'm bored in work - 8am on Sunday

same here, except i shouldn't be here, already worked my mon-fri, then saturday as extra...

oh well, it'll be a short week next week in lieu

[DarrenSV650S]

I bought this one last night - Clicky
Good or bad choice?

[the_lone_wolf]

Originally Posted by DarrenSV650S

I bought this one last night - Clicky
Good or bad choice?

that's SPCO - single pole change over - means that there are two positions for the switch to be in, when the coil is off it connects one pin to ground, then when it's open it disconnects that one and connects another. you can use it, but it's extra capabilities are surplus to requirements

the most basic one for your application is a single pole normally open SPNO, which is a simple 4-pin relay that connects two pins internally when a voltage is applied across the other two

http://www.maplin.co.uk/Search.aspx?...N00AW&DOY=13m7

Originally Posted by the_lone_wolf

the most basic one for your application is a single pole normally open SPNO, which is a simple 4-pin relay that connects two pins internally when a voltage is applied across the other two

Don't forget the 3 pin variety that shares a common ground with the coil.

[the_lone_wolf]

Originally Posted by Baph

Don't forget the 3 pin variety that shares a common ground with the coil.

it would be poor practice to share a common ground between the high and low current circuits if you are splicing into the vehicle wiring and not adding uprated cable shirley, that's the whole point of using a relay

Originally Posted by the_lone_wolf

it would be poor practice to share a common ground between the high and low current circuits if you are splicing into the vehicle wiring and not adding uprated cable shirley, that's the whole point of using a relay

That's the reason that Ford use diodes.