Dax electrical gremlins

I wonder if one of you experts could help me out with this issue?

I have a 1976 ST70 which I assume is 6 volt. Everything was fine last year but just about to get her MOT'd for the summer and it's doing weird things. The symptoms are as follows:

1. Firstly let me say that the battery is 2 or 3 years old. However I charged it off the bike last night and the charger indicated it was fully charged.

2. However when I turn ignition on the neutral indicator light doesn't always light up. It's weak and seems to flicker.

3. If headlights are off then the brake light illuminates (from either front or back brake) but not very brightly.

4. With headlight switch in the first 'on' position the rear light illuminates,(but not very brightly) but no front light. (I'm not sure if the first 'on' position is only supposed to work the rear light anyway).

5. With headlight switch in the second 'on' position both front and rear lights illuminate but not very brightly.

6. If I operate the brake/s with headlights in either first or second 'on' position the rear light seems, if anything, to dim. From above it looks like I can see a second filament operating but it seems to dim both filaments so that overall it dims when brake is operated.

7. The horn operation is intermittent. As of right now it doesn't work, and if I press the horn the neutral light dims or goes off altogether.

8. The bike has also developed an intermittent misfire under load although I suspect this is a completely different issue. Thought I would mention it though.

I know nothing about electrics but suspect that it will be something simple like a bad earth. Any ideas? And if it is a bad earth or something where and how do I check for that?

Lastly, as we know, 6v lights are rubbish and mine (as I assume everyone's do) dim to nothing when the engine isn't revving. Can the electrical system be up-graded or is that not possible?

Many thanks in advance.

Cheers

Rob

Hi Rob,
some symptoms you're talking about are typical on 6v bikes. (dimming, flickering neutral,...)
Due to the number of different issues, yes it could be a bad earthing / connection or short circuit.

You could upgrade to a 12v ignition system depending on the type of crankshaft you have in your engine.
It's not all that easy though...

Did you recently paint the frame, driven in bad weather, washed with plenty of water?

I'd check the horn first if I were you.
Also, check the condensator: can you see spark under the flywheel when the engine is running? (test in a dark room)

Does the horn work with the engine off? It should, so does the brake light. As these run from the battery.
After that, check the ignition / light coils and the complete wire loom.

Thanks Waynus

I have a new battery on order. Once I have eliminated that potential issue then I will work through your suggestions if the problem still persists.

Will post results in due course.

Rob

Just fitted the new OEM battery and all of the issues seem to have disappeared. The previous battery was three or four years old. It had been playing up a little in that the charger didn't register any lights whatsoever when I connected it to the battery. However when I took it off the bike it seemed to connect to the charger and charge just fine. Charger indicated it had full charge the next day but perhaps it wasn't holding the charge and going flat straight away? Anyway, all the issues listed above appear to have been resolved with the new battery, which was only £12.00.

I have yet to take it for a ride so time will tell if the mis-fire under load was also related to the bad battery or whether that is something unrelated.

Cheers

Rob

If all the problems are solved by replacing the battery, it had a bad connection / short circuit somewhere.
Otherwise, there's no reason for misfiring etc.

Further update. As previously posted, the new battery fixed all the electrical issues such as lights dimming when brake light operated, and intermittent horn etc. However the misfire continued and actually the bike died. Traced it, I think, to a loose, badly fitted spark plug cap. Have re-fitted the cap, (trimming a bit off the HT lead to give it a fresh bite), and it runs fine again.

So far anyway! I'm going to get a new plug cap in the next few days just to be sure.

You're doing great, keep up!
If in doubt with any wire, switch, connector,... replace it for a brand new one.
This will save you the same issues for the future.