callum12 256 #1 Posted May 18, 2015 hi all,I was at a vintage car rally yesterday and i picked up a 335hz 12v hella horn, I am trying to find out if I need a relay or not? some people seem to say you do while other people say a good 5A switch will do it. I will of course be fusing the horn.also would i wire the switch on the positive lead? thanks for you help,callum Share this post Link to post Share on other sites
squonk 38,952 #2 Posted May 18, 2015 I would put a relay on it. Those 5 pin relays most cars use are plentiful at any Pick your part yard. Most of them have the pin diagram right on them. I have a drawer full of them. Share this post Link to post Share on other sites
callum12 256 #3 Posted May 18, 2015 I think I've got a few somewhere, what sort of amperage is a horn? thanks for your help,callum Share this post Link to post Share on other sites
squonk 38,952 #4 Posted May 18, 2015 Horns vary. I've seen some as high as 15 amps Share this post Link to post Share on other sites
Save Old Iron 1,563 #5 Posted May 18, 2015 given the short wiring run in the average LG tractor, and considering the horn will likely be less than 10 amps, forget the additional wiring required for a relay. Wire the horn thru a fuse then thru an automotive quality momentary switch directly to the horn. 3 Share this post Link to post Share on other sites
Save Old Iron 1,563 #6 Posted May 18, 2015 homework time for yougoogle "335hz 12v hella horn"find the manufacture's data for power consumptionif power consumption is in watts, divide that number by 13.8 to give amps drawn when vehicle is powered up.double that amp draw (for a generous safety margin) and select a switch for the doubled amperage. 4 Share this post Link to post Share on other sites
"D"- Man 827 #7 Posted May 18, 2015 (edited) I don't know what sort of steering wheel your tractor uses, assuming it's an A-800, but I am planning on using a Grant style steering wheel with a Corvette horn button/switch on my 18 Auto Resto-Mod, Mark. Edited May 18, 2015 by 23 Automatic LSE 1 Share this post Link to post Share on other sites
callum12 256 #8 Posted May 18, 2015 (edited) yes it will be my A-800, that steering wheel will look really nice. i was going to have the switch under the the aluminium dash box so it is out of the way but quick to get at (not that much happens quickly on a tractor!).thanks for your helps save old iron, finally some homework i want to do!!Callumedithere's my homework sir, 66W so 4.78A, i'll go for a 10A plus switch i think, maplin will do them. thanks for that. Edited May 18, 2015 by callum12 hand in homework Share this post Link to post Share on other sites
squonk 38,952 #9 Posted May 18, 2015 Using a relay takes 2 more wires. Big deal. I'd rather have the relay. Share this post Link to post Share on other sites
callum12 256 #10 Posted May 18, 2015 I see your point, it is nice having that extra protection, but my WH does have to live outside sometimes (this is in the UK too). even though it will be well covered I rather keep electronics to a minimum really. If the horn only draws 4.7A and i use 25A switch with fuse i don't foresee any problems. thanks for your help,callum Share this post Link to post Share on other sites
squonk 38,952 #11 Posted May 19, 2015 A 25 amp switch would be pretty big Share this post Link to post Share on other sites
Save Old Iron 1,563 #12 Posted May 19, 2015 (edited) A 25 amp switch would be pretty big you know the old saying...big switch? use a big fuse! Edited May 19, 2015 by Save Old Iron Share this post Link to post Share on other sites
callum12 256 #13 Posted May 19, 2015 haha, i'm using wire from pylons as well!the switch i've got for my headlights is a 25A toggle switch, i think it is a bit bigger than the standard I'm not sure. a momentary switch of the same value might be quite a bit bigger possibly? I've found some 10A vandal proof switches! they look quite cool and have a cool name. Share this post Link to post Share on other sites
george.stringer@frontier.c 0 #14 Posted May 31, 2015 You can go either way with your horn. If you decide to not install a relay you will need a switch capable of passing high amperage. If you install a relay it will cut the amperage at the switch and you can use mini push button switch. Carefully remove the tin cover on the relay by bending the attaching prongs straight. Use an ohm meter to see where the current goes when the blade on top of the coil is closed. That post is where you attach the wire going to the horn. Two other wires are needed - one to + bat and one to - ground. Put your horn switch in the ground circuit with your fuse in the + circuit. If you use a Delco Remy horn it can be mounted on the hood hinge above the axle. I will insert some pictures. If you have more questions email me at george.stringer@frontier.com. The picture with my hand in it shows the horn position with the hood closed. George Share this post Link to post Share on other sites