Rewiring my 1966 Mk 3 NC

[linker48x]

Hi guys, I need some help sourcing appropriate switchgear for my Ducati single. I have a 1966 Mark 3 250 narrow case. This is the one with the non-battery (AC or "magneto") ignition. I have installed an Electrex streetbike ignition supplied by Nigel, and he and the ignition are first rate. I am also using a capacitor and no battery with the Electrex. The engine side of that ignition system works wonderfully.

I am looking to re-wire the light circuits now, in a simple way, so that I can power the headlight and tail light and brake light with the positive side of the alternator, and ground them with the negative side.

I could do that with modern looking switchgear, but I am hoping someone here can help me out with sourcing classic Italian-looking switches I need to rewire my 1966 NC Mark 3's lighting circuit.

The Mark 3 is the one without a battery, and because it powers the tail and stop lights off the ground, the headlight switch does not have a connection for these lights. Also, because it powers the tail and stop lights off the ground wire, it has a stop light switch that is always "on", but shifts the ground connection from the frame to the stoplight depending on whether the brake is on or not. I want classic Italian looking switches for the headlight that has a connection to take the current for the taillights when the headlight is on, and a stoplight switch that is off until you step on the brake, AND that mounts like the stock one, on the stock bracket.

First , I need a stock looking, Italian headlight switch for the handlebar that allows me to take power from the headlight circuit after the switch is turned on, before the dimmer switch splits the power to high and low beam, to power the tail light. This can be a switch that comes with a dimmer switch built-in, or with a separate dimmer switch. If separate, I will need the separate dimmer switch too. I assume this is a switch that would be standard on a Ducati single with a battery, but I don’t know that. The stock switch uses the ground to power the stoplight and taillight and so it has no way to take power from the + side for the taillight when the headlight switch is on. The stock switch incorporates a dimmer switch that splits the power only into into hi and low without a connection for the tail and stop lights.

I also need a stop light switch hopefully that mounts like the original, on an 8 mm threaded post facing forward, toward the pull of the brake pedal. The original is always on, powered from the ground. I need an “ordinary” one that is off until the brake pedal is depressed and it turns on. Again, I assume this is a standard Ducati part from a bike with a battery, although I don’t know that. I have a generic British stoplight switch that works the correct way but it doesn’t look right on the bike.

Anybody have ideas on what switches I should use, and where to get them?

[bodge]

this lot are probably the best source for original pattern parts https://www.ducativintagestore.com/apri ... esmo_mark3 depending where in the world you are.

not cheap and im not enough of an expert to say this is exactly the part you need for authenticity but they mention mk3 in description. other nc parts are in the ducati 1962/68 section

[Bevel bob]

Hi, Most of the 250 Narrow case Mark 3 's that were imported into the uk would have been the battery version , as battery less bikes were not popular here due to unreliability issues with ET systems tried on other makes. Also ET Ducati's had advance /retard systems that could make starting a hazard. I hope that the Electrex system gives a better result.

[JimF]

“I need an “ordinary” one that is off until the brake pedal is depressed and it turns on.”

Yes, i think you are correct. You need a Normally Open or NO switch. It’s unclear which type the Ducati Vintage Store is selling on their site.

I believe the original switches we see on our Ducatis were one of two possible flavors: Normally Open (NO) or Normally Closed (NC).

The normally open switch is used on the “DC” bikes. A 6-volt ‘hot’ wire goes to one switch terminal and the other terminal goes to the brake light filament (higher brightness) of a dual filament taillight bulb.

The NO switch closes with brake pedal depression and sends power to the brake light.

The normally closed switch is used on the “AC” bikes. The ignition coil’s ground wire is run to one terminal of the switch and the other switch terminal is connected to ground. Because the switch is normally closed the ignition coil works it’s magic and the motor cycle runs.

The NC switch opens when the brake pedal is depressed which opens the ignition circuit which will kill the engine UNLESS you run another wire from the ignition coil’s ground terminal to the brake light filament.

When the brake is depressed the coil sees another connection to ground through the bulb filament, and the motorcycle continues to run while the current makes the brake lamp light up.

With the NC switch if the bulb burns out the motorcycle will die if the bulb filament breaks or burns out.

Some Ducatis were equipped with an emergency switch which restored the coil’s ground connection which in turn restored the ignition system’s operation if and when the brake light bulb would fail. A driver could flip the emergency switch and in turn operate the motorcycle without the benefit of a working brake light.

[ducwiz]

As far as I see this figure shows the original schematics of the "AC" type 250 NC singles:

250scr till 92171- loom-schematics.jpg

But, as I understood the Mk3 now is equipped with an Electrex alternator/CDI system (STK-160 or 161?). This modification needs a modified wiring anyway, so the entire ignition part and the entire alternator in the schematics can be neglected, and in turn also the "specialities" concerning the brake switch, grounding scheme of the ignition coil (which btw is gone with the Electrex anyway), etc.

Hans

[JimF]

I agree Hans,

I was merely trying to point out why there are two styles is switches and which one was needed.

Another “plus” that comes with using the NO switch and DC system is that it’s possible to use LED taillights (brighter, more robust and uses less power than incandescent light bulbs).

Jim

[linker48x]

Thanks for your input, everyone who has posted. As I said, I want to source a headlight switch and a stoplight switch. It is my understanding that the linked stoplight switch on the Ducati parts/Aprilia electrics site is the same as I have. As I understand it, the Mark 3 and the scrambler both used the NC stoplight switch, and the one in the linked listing appears to be that one. I had already seen that one and concluded it wouldn’t work.

Incidentally my Mark 3 has an accessory toggle switch mounted in the top shock mount gusset to let the engine run, if the taillight burns out. I seem to recollect this was a standard mod back in the day.

So, any thoughts about locating a handlebar mounted headlight switch that looks vintage Italian, and a NO taillight switch? On the headlight switch, if I can’t locate a suitable switch, I’m thinking I’ll use the stock switch I have now, and take a hot wire for the taillight off one of the low or high beam wires, so it will work on either low or high beam, but not both. Shouldn’t be a problem, I can’t imagine actually riding this at night. On the stoplight switch I suppose I could use something else but it’d be nice to have something that mounts in the stock location.