Horn relay

If the horn sounds ok it's not short or jammed, therefore it is either a battery issue or a charging issue.  A relay will not help the situation as the current the horn requires still has to be drawn. 

Some checks;

 Is it the correct horn for your system i.e. 6V?

 Does it work repeatedly on another battery?

 Is the battery getting charged?

 Is the battery capable of sustaining a high discharge i.e. the right size, old?

How often do you use the Horn?

... if it works once then takes a while before it works again I'd suggest the battery is either too low a capacity (amp-hour) or is on its way out. I have a 4AH alarm type sealed battery on my ES2 and it works the Altette horn fine (quite loudly) several times in succession even after standing for months.

Hi Ian, think I read in one of Al's excellent pieces that actual alarm batteries are not really up to the job for a bike, so it might be worth looking into that.

It is as Jonathan says, no point in a relay. Is the battery of sufficient Amp Hourage-charge? In the first place. Alarm batteries, especially if on the way out would be of limited usage, especially if the horn was  needing high power or maybe wrongly adjusted. The charging of the battery on the bike could be an issue with regard the horn but a low or failed charging would be an issue in its own right.

I wouldn't use one if I was dependent on it for sparks but find they work well for the dynamo setup on my ES2. They hold their charge very well and are small and easily fitted in a dummy Lucas case.

I don't see why they would be any worse than the Cyclon type that many people recommend.

I'm with you on this one, Ian. I've been using alarm batteries on 6 volt bikes for a decade or so. They last longer, take up less room and are less messy than standard lead acid motorcycle batteries. Best thing since canned beer in my opinion. 

... the canned beer!

Canned beer-to be avoided if you can! 

Now batteries, if we look at the charge characteristics of our batteries, the lead acid was made to vent if over charged and it often did back in the 50s and 60s when they were current.

Cyclons have a Voltage charge limitation this is why they are useless on the traditional 6V switched alternator change control, they will very easily over charge on longer journeys. So Cyclons need to be used with decent charge regulation. 

Alarm batteries, depending on their size have a limited charge current. You will get away with extra current with these for a while. But a 50 mile or more journey at speed could start to over charge. Again depending on your charge regulation. A few of these over-charging's you will 'get away with'. With any battery it is always useful to find out its charge characteristic and if you must buy from a dodgy source ie flea bay or Auto jumbles, I would always advise you to have on the receipt-FIT FOR AUTOMOTIVE USAGE.