EL018 ELECTRICAL

I have owned a 1959 Venom for just over a year and have been plagued with it wrecking batteries. 
Initially it came with a standard 6v set up, 35W Miller dynamo (but with top mounted cut-out removed) & Lucas regulator box. 
Shortly after I bought it the battery expired. Fine I thought, the bike had been standing for some time, it was just an old battery, so I replaced it, having checked the wiring to ensure it was +ve earth (I read that the very early ones were -ve earth, but this didn't seem to apply to me, as the wiring conformed to the diagram for +ve earth/Miller dynamo/Lucas regulator in the Red Book, & the old battery had been wired in this way). 
This battery also quickly expired. Ah, I thought, so it is -ve after all ( I might add that the polarity of the battery seemed to have changed!). 
I wired the next one the other way round & killed that one too! Incidentally the ammeter had always shown a + charge with the lights on but no engine, I quickly worked out that this was because the ammeter (Miller) had been wired the wrong way round (a la Lucas), so that was corrected. I began to suspect a problem with the regulator, and decided to cut my losses, lose the regulator, upgrade to 12V & fit a JG unit. 
All was fine over the summer, but as the dark nights began to draw in, after a couple of night rides the battery was flat again, despite the fact that the charging circuit appeared to be working (though the ammeter needle flickers so much it's hard to be sure), & a new belt had been fitted). 
I charged the battery up on the bench last week & refitted it to the bike, but only tried to use it today. As soon as I connected the battery, it started to bubble & give off gas and the cell nearest the cathode was soon warm to the touch, so it was quickly disconnected! 
So, am I being dim somewhere ( I don't claim any great skill with electrics!)? 
The wiring from the +ve terminal is red & I have traced the red wires to a frame mounted earth so have to assume it is +ve earth. I might add the wiring is in good condition & obviously replaced @ some time. Have I fried the JG unit or reversed the polarity of the dynamo? Is it possible to run the bike without a battery, it seemed to power the lights Ok on the generator with a flat battery? - Steve Orme 2/2/2004

my thoughts are that after you fitted the JG unit you weren't actually getting any charge into the battery, but you had stoplights, horn etc because the battery was charged initially. When you started using the lights the battery soon ran down. Vibration does make the ammeter flicker in a way that looks like you are getting a charge, but when it is a real charge the ammeter becomes a bit steadier and shows a distinct positive swing. The reason why you weren't getting a charge could be a fault with the wiring or any of the components, but you'll probably never find out now.

When you re-connected the charged battery it does sound as though it or some other connection was wrong, and damage has probably been done.
The only way forward is to check everything from basics, and if at all possible using a voltmeter (less than a tenner nowadays for a fabulous digital one).
First double-check whether your JG unit is intended for +ve or -ve earth. Whichever it is determines which way round the battery must be connected. The JG can't be reversed and will die if you try to.
Wire a headlight bulb across the battery and run the battery down to a glow. Then disconnect the bulb, charge the battery for about half its capacity (eg 2 hours at 3 amps) then wait an hour then check it says around 12.6 volts and if so reconnect the bulb and check it shines bright for an hour. If it does, your battery is good enough for the other tests.
Use it to test that the dynamo motors; and in the right direction - see the red book and other Q's but you'll have had to change the dynamo's wiring to fit your JG so you'll need to translate the instructions for testing the dynamo.
Run the battery down a bit so it is less than half charged.
Then install everything on the bike, triple checking every connection matches the JG instructions and that you have the battery the appropriate way round. (And that the JG has a really good earth). Don't make the JG's connections, but rather first just make sure that the ammeter shows an appropriate discharge with the lights on; and that everything works.
Then connect up the JG. If you get sparks or fizzing etc it is faulty. If OK, and no discharge is shown on the ammeter you can start up.
There may be no charge at first, but switching the lights on and a few revs should show the ammeter swinging from discharge to charge as the revs rise. If they don't then the JG unit appears not to be doing its job.
If it seems OK, and if you have a voltmeter check the voltage across the battery rises to between 13.5 and 14.5 volts as you rev the engine. If it does then everything is fine.
I don't think you can run a JG without a battery; and you'd blow bulbs if you had neither regulator nor battery. - TW 3/2/2004

After I had stopped panicking & slept on the problem, it became obvious that I WAS being dense, & it was a direct short to earth, & the only component I could imagine being that vigourous was the horn (still 6V on 12V system). 
Sure enough when I dropped it off & tested it that was the problem.. I took the opportunity to trace the wiring (since I had the seat & tank off to check the loom anyway), & reached the conclusion that the bike is definitely +ve earth. With the horn replaced (a car 12v one from Halfords, with the old "aesthetically pleasing " on disconnected but fastened in front to hide it!), battery recharged & horn button/dip switch cleaned up everything was hunky dory again, & the ammeter showed a steady charge. 
Just goes to show that you need an open mind for electrical faults, it's easy to take on a mind set which leads you up the garden path! - Steve Orme 9/2/2004