1973 3C coil failure?

[thore bergsaker]

Hello, suddenly I lost the left and right cylinders on.my 3C while riding. It has a twin coil setup, the beige ND coils. Witt ignition. All.leads seems to be in place. There are three leads coming to the coils. One goes straight to the top of the L/R cyl coil, one goes straight to the bottom of the centre cyl coil and the third is split in the junction with one lead going to the bottom of the LR cyl coil and one going to the top of the centre cyl coil. Where would you start?

 

[Paul Marx]

Mesure the resistance between the two terminals on the coil, primary winding. It should be low, 4 or 5 Ohms maybe. Then measure between one of the terminals and the HT lead, it should be high, maybe 17 000 Ohms. If that measures up, the coil is OK.
Paul

 

[Rob]

A lot depends on which Witt ignition you have (DMC 1 or 2), and how it was connected to the bike's wiring. But I'd check that you have 12v on the 'split wire' to the L/R coil with the ignition switched 'ON'.
ND coils are very reliable.
The Witt installation instructions provide some troubleshooting tips -
https://laverdaforum.com/resources/categories/moto-witt-dmc-ignition.12/

 

[Schurminater]

Also check the simple things first like plugs,caps and leads

 

[sfcpiet]

Check if the coil still works?

First, power supply to coils. Yes>check coils. No>check wiring. Coils work, still no spark>check HT leads and caps. Coils don't work>replace.

As both cylinders failed, the cause is likely to be either the coil itself or the wiring supplying the current. Very unlikely that both HT leads and/or caps should fail simultaenously.

As Rob states, the ND coils are almost indestructable. The weak points are the wiring connections, these are known to fail, once the warranty has expired...

The original wiring for the original pick-ups will be far beyond its best-by date by now, not unusual to find a short circuit there as well.

piet