One thing to watch out for.
Your 69 would have originally had 12 volt coils.
Using these wired in series with an electronic ignition will massively reduce the quality of your spark as well as prematurely burn out your ignition’s black box.
Most manufacturers specify a total coil resistance of between 3 and 4.5 ohms.
The 12 volt Lucas 17M12 (LU47276) coils that your bike would have had originally are rated at 3.3 to 3.8 ohms.
So stacking two coils in series, that‘s 6.6 to 7.6 ohms in total - which far exceeds the recommendation.
The bike will still work fine for years, but it will burn out your black box eventually.
You may well have addressed this and already fitted the later 6 volt Lucas 17M6 (LU47275) coils, but I wanted you to be aware of this issue, as I’ve come across it a few times.
Check your charging system and battery - I don’t feel you’ve dug deep enough on this.
Looking for three charge states (engine off, idling and at high revs) will help us determine that your charging system is ok:
-1-
Lead acid (including gel, AGM, flooded and drycell) are 2.1 volts per cell, so you should be seeing 12.6 volts DC at rest with your meter across the battery positive and negative terminals
-2-
With a lead acid battery at idle with the lights off you should see 12 to 13 volts DC with your multimeter across the battery.
By design, and with a healthy pair of coils, you are typically taking out more than you are putting in with the standard charging system.
-3-
At 3,000 to 4,000 rpm you should see 14 to 15 volts DC with your multimeter across the battery.
The actual figure sill vary depending on whether you have the original zener diode fitted, or are using a combined reg/rec.
With a digital multimeter, you’ll probably see quite an erratic meter reading at higher revs.
This is because of interference picked up by the test leads (think of them as aerials attracting interference).
Keeping your leads short and away from everything else on the bike (especially near the coils and spark plug leads) will help stabilise your reading.
The next thing on my list of quick checks would be the ammeter.
With the exception of the horn, the full current draw of tge bike is pulled through this.
The coil in the meter will only last forty years or so before it starts burning out (bloody Lucas and their terrible unreliable electronics again)
You can easily bypass the ammeter (either join the wires together, or if it’s easier jumper the terminals using a wire with crocodile clips on each end)
This will easily rule in or out another questionable area.
The final quick check is around the bullet connector that feeds the battery positive to your headlamp bulb.
These, over years of the headlamp going in and out of the headlight bucket wear over the years, as there is no strain relief on the bullet.
If this connection is bad, it will give you problems, so it’s well worth checking the quality of the bulked and the wires.
The rest of the wiring on the early bikes is pretty rock solid and reliable:
