'69 Fastback Ignition problem

storm42 said:

Bad earth?

What voltage do you get between the positive terminal of the battery and the engine case or frame? (Or negative if positive earth) and does this change when you turn the lights on?

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Yes and clean up your fuse contact points in the holder. Actually clean up everything electrical.

storm42 said:

Bad earth?

What voltage do you get between the positive terminal of the battery and the engine case or frame? (Or negative if positive earth) and does this change when you turn the lights on?

Click to expand...

Yes, it can do on a very old bike even with clean connections. The copper wire can become greem/brown/ black and there can be as much as a 2 or worse, volts drop which can cause you all sorts of problems.

As I said before, take a wire from the battery negative directly to the white wire on the Boyer.

Take your fuse out, which will disconnect the NU (brown/blue) that feeds everything else on the bike.

Go for a ride - you should get a couple of hours from a healthy new battery with no trouble.

If it dies after a few minutes, you know it’s an issue with the electronic ignition or your coils.


From what you are saying, it doesn’t sound ignition related to me.

gtiller said:

As I said before, take a wire from the battery negative directly to the white wire on the Boyer.

Click to expand...

I would suggest if that doesn't cure the problem then connect a wire between battery positive, Boyer box red and the second ignition coil. As the 20M3 Commando had its condensers attached to the rear airbox plate some distance away from the coils, therefore, the condenser 'earth/ground' (red) wire cannot be connected to the second coil negative terminal (Edit: or attach the blue connector to the condenser pack earth tag) as it says in the Boyer instructions:
"13) Remove the red wire from its earthing point on the end of the condensor pack. Reconnect this to the + marked terminal on the left-hand ignition coil."
.
"16) Connect the red wire from the transistor box as follows: first (Blue) connector to the earth tag on the end of the condenser pack, second (red) connector to the + terminal of the left-hand ignition coil with the red wire already connected to it."

Thanks everybody for their input I think I have finally found the problem, I had done what Grant had suggested run a power wire from the battery, I had also run a direct earth from the coils back to the battery what I couldn't understand was that I was getting strangely different voltage readings from different sides of the wiring connections, as a last resort I decided to circumvent the amp meter and wella a loose nut on the amp meter connection, it would pass enough for me to get a meter reading but as soon as the load went on nothing, again thanks everybody!

If it's any consolation, my brother shelled out on a new starter motor for his Hinckley Triumph because it would click but not turn over on a new, fully charged battery.
When that didn't fix anything, I was 'invited over'... The new battery terminal screws were longer than the originals and bottomed out before clamping the terminals.
Oh, how we (well, me actually) laughed about that one...