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Sprite Twin Tone Horns

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Yes, you definitely need a relay. The wiring diagram in the shop manual shows how to wire them, and it shows the relay as well. This diagram can be found in the Haynes manual too. The horns themselves are simply wired in parallel; the relay switches them in the usual fashion.

I'm away from my office now, but if you need more info let me know and I'll scan the wiring diagram. Every Sprite owner should have a copy...!
 
I'm putting relays on mine - just in case - Classic Motorsports Magazine did it a couple of months ago - I have it and can scan it if you can wait till next week - it didn't have a lot of technical info though.
 
spritenut said:
I put twin horns on my 67. I just added wires from the first horn to the second.
It works, no relays.
Click to expand...

I don't doubt it will work for a while, but I suspect you will fry the contacts in the horn button or steering brush eventually. Those little suckers pull a lot of current (stock ones are ~12A peak, ~6A average, EACH), and the fact that they are an inductive load will cause quite a bit more sparking at the contacts than normal. I'd really recommend putting in a relay--cheap and simple.
 
I'm curious...

I researched horns when I was at that point in my '63 Midget restoration....the 2nd horn was a factory option, they all came from the factory with 1 horn unless specified.

The wiring diagram didn't show any difference between the single & dual horn setup other than the wires between the 2 horns.

So, I ordered a set of new horn brackets, a set of new horns & made a wiring harness from one horn to the other out of the correct guage & color wiring.....& hooked it up.

Why won't it work?
 
As stock, the full amperage goes through the switch, which eventually causes it to fail. It'll fail even faster, with double the current.

So, as with uprated headlights, electric fans, electric fuel pumps and anything else that pulls a lot of power, a relay can be used to minimize the current carried by the horn switch contacts, and to reduce voltage drop.

Not totally necessary... just a little extra protection.
 

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So, why do all my MG dual horn set-ups still work 30 years after the factory closed? Don't see relays in the wiring harnesses
 
Maybe you've been keeping them in shape by using them regularly? :wink: Seriously though, I thought it was a pretty common failure. Didn't Jack have to redo the horn contacts on Miss Agatha?
 
tony barnhill said:
So, why do all my MG dual horn set-ups still work 30 years after the factory closed? Don't see relays in the wiring harnesses
Click to expand...

Tony,

Although I tend to agree with you on your comment, I'm not so sure I'd EVER trust the judgement of anything associated with an installation that incorporates ANYTHING LUCAS!! :wall:

They didn't earn the "Prince Of Darkness" nickname because of their reputation for reliability!! :eeek:

I think I'd put a relay in JUST TO BE SAFE! That and some additional fuses, some fusable links, and a generous supply of wire, fuses, elect tape, and a Fire Extinguisher in the trunk!! :yesnod:

"Better safe than stuck on the side of the road...." :savewave:

"Cheers!" :cheers:

-Bear-
 
See, whenever I have the rare Lucas flare-up, it can be traced to poor maintenance...usually, its a corroded connector or ground...occasssionally, an instrument will finally - after 30 years - fail....but, Lucas problems? No, not on a properly maintained car....& I 'll bet the horn system just like everything else was over-designed at the factory.

Remember, I'm the guy who took off across the US, Canada, & Alaska in my RV on a 15,000, 6-month trip with only my '79 MGB for daily transportation....true, I'm its only owner & have done all my maintenance on it religiously.....the only thing that failed was the OE air pump that I forgot to do maintenance on before we left...I'm still convinced that, had I sprayed white lithium grease up inside it before we left, it would still be working!

I'm not gonna worry about my horns.
 
Hi Tony,

:iagree:

I agree that I wouldn't worry about your factory installation. I TOO tend to leave things alone that haven't been tinkered with. (My '60 BugEye, '47 Austin10, & '57 Austin FX3 Taxicab are all 100% stock!)
"If it ain't broken don't FIX it!!" :nonono: :nonod:

BUT whenever I get in there & modify anything I try to upgrade it to a better quality installation that originally designed.

I have to admit that I've had pretty good luck w my Lucas electrics. Haven't really had reason to complain to date.... (Wait! Where's some WOOD?!? Quick!!) :wall:
BUT I do tend to be a bit of a "Worry Wart", so anything I can do to safeguard an installation simply provides me with a better night's sleep. :sleep:

Simply put, if someone asks me how to do it, I'd have to recommend spending a few extra $$$ up front and do an extra safe installation. I'd hate to make a recommendation that might fail them at a later date. Besides, it is cheap insurance that'll pay for itself with the 1st missed tow truck call! :driving:

"Cheers!" :cheers:

-Bear-
 
I have installed dual horns, and/or air horns with out ever using a relay.
Sure it's a good thing but the factory never did it. and twin wind tone horns were optional on most Brit cars back in the day. They just added a wire jumper from one to the other.
I never had a failure and I have been driving a Sprite for 36 years.
 
The simple answer to Tony's question is (and this is my suspicion; I have no hard information) that the MGB horn buttons were probably designed to handle the current. It's also possible that Lucas got sensible at some point and created a horn that didn't require half the output of the Hoover dam to run it. I see no reason why a car horn should require more than a couple amps, but the original Spridget ones surely did.
 
Thannks for the good info, I think I will not risk damaging the horn switch and install the relay. My shop manual does show a relay for the twin horn option, but wasn't real clear about the wiring. Your diagram provides the info I needed.
 
So, does anybody know where to factory would've put the relay?

& which Lucas relay it was?
 
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