b.s.a.c15 won,t start

[mossy]

hi there no wonder i can,t get my c15 started i think i,ve got a serious electrical problem i hope someone can advise me differently, so here goes. i thought i,d got a spark at the plug (well i did have but it didn,t last) i have just charged my battery up before trying it on the bike, with a 6v tester accross the battery termnals its fine but when i turn the ignition switch to either on or emergency start position (new switch  and i,ve tried the old one as well ) the tester light goes  really dim and the c.b lead( black and white) is only sometimes  live and when you open the points by hand you get a spark when the spark plug is earthed to the engine then it just disappears until you disconnect everything and start all over,then you get a spark for a little while. only the battery power has all but diminished now.i have tried two coils , &  two dizzies. i thought maybe the wiring harness was shot but took it off the bike and tested it on the bench putting a tester to each end of the wires and all seems fine except the small rectifier post was only live some times (i,ve wire brushed it all of and now that seems good as well. the only other thing i,m not sure about is the three wires out of the alternator as they  could be connected incorectly but would this really make a big difference,as i thought they were for charging and lighting only. any advise would be helpful,thanks folks

[R]

How good is this battery you have though - its quite possible to charge up a battery with a dead cell, so it appears charged, but it can't put out more than a trickle of power, sometimes for only a few minutes even. Does the headlamp come on good and strong, and stay strong for a few minutes at least of test ?

If the headlamp is strong, can you directly connect power to the points and coil, and bypass all the switches and harness, and see if that improves things.

Good Luck - aren't electrical problems fun !

[R]

Its also possible you may have an electrical short circuit, which is why the lights go dim. ?

If you had an ammeter in circuit, the needle would then go solidly to the 'discharge' side, showing that power is being drained out of the battery rather rapidly. The only solution to this, if this is indeed happening, is to sort through all the wiring and find one that is wrongly connected, or a wire that has been pinched or cut and is allowing power to short to earth.

As previously, GoodLuck...

[Don Vosper]

A few days since the first post so I wonder if it's going yet.
6V systems take quite a lot of current so a poor connection somewhere can cause quite a large voltage drop.
If you suspect the alternator connections perhaps you could temporarily  disconnect it once you've recharged the battery.
Don
I see that the c15 is positive earth. Silly question, but you do have the battery the right way round?