'68 350 Scrambler-12V conversion questions

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dlearl476
Posts: 25
Joined: Thu Feb 28, 2019 12:28 am

'68 350 Scrambler-12V conversion questions

Postby dlearl476 » Thu Oct 10, 2019 2:23 pm

Hey all, I'm most of the way to firing the Scrambler, but I have a couple of questions: I have a 12V conversion and new headlight/wiring loom sourced from Phil @ Road and Race.

Going off the '68 wiring diagram (6V-which is all I've got) in place of the 2 yellow + 1 red coming out of the stator, I've got 2 yellow, 1 red, and 1 blue. I've also got a brown wire coming out of the loom from the terminal block in the headlight. The 12V VRs I sourced (1Mototrans, 1 DM) both have terminals for 2 yellow (check) 2 red (check) and 1 brown.

So, I'm assuming the brown wire from the terminal block goes to the brown terminal on the VR? Where should the blue wire from the Stator go?

Using a combination of my old loom and the 68 wiring diagram I think I've got everything sussed out, save this last mystery and I don't want to hook up the battery and give it a kick until I know I'm not going to fry anything by incorrect connections.

Thanks.

Video of first firing after 40 years to follow (with any luck!)

dlearl476
Posts: 25
Joined: Thu Feb 28, 2019 12:28 am

Re: '68 350 Scrambler-12V conversion questions

Postby dlearl476 » Thu Oct 10, 2019 2:28 pm

Oh, one more Q?

Both my original loom and the new one have a pair of wires, one blue one black, unterminated in the headlight running back to a likewise unused double terminal block at the battery/horn/brake light switch location. Can anyone tell me what these are for?

TIA

dlearl476
Posts: 25
Joined: Thu Feb 28, 2019 12:28 am

Re: '68 350 Scrambler-12V conversion questions

Postby dlearl476 » Thu Oct 10, 2019 2:33 pm

PS: This is the 68 Wiring Diagram I'm working off of.
image.jpeg
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ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: '68 350 Scrambler-12V conversion questions

Postby ducwiz » Thu Oct 10, 2019 6:46 pm

It is not clear for me which conversion components you have at hand. Is it the entire conversion kit http://roadandrace.com.au/alternator_conversions.htm from Road&Race? If so why do you have or even need 2 addional VRs? If you want to connect them to your original 6V alternator you have to identify the precise types (look for stamped ID codes etc.). I'm also afraid that they will not work with the new R&R alternator. I recommend posting more details about the components, and adding some photographs, before firing up the bike and trying to produce electric power.

I understand that your original alternator has 4 wires - the usual 2 yellow and one red, and an additional blue wire. I identify this as a Motoplat alternator/CDI supply combo, not the usual Ducati 3wire type. The blue wire carries the extra power for the electronic CDI unit. This type of alternator did not exist in 1968. Some previous owner must have installed it, in 1972 or later. If you don't run the bike with the Motoplat CDI, this wire is useless. But: with the engine running you have up to 400V AC on it! So insulate the open end properly and stuff it away. Btw, the maximum power output of the Motoplat alternator is 75Watt, while the Ducati type produces 90W.

A 12V conversion of the 6V alternators can be done in principle, still keeping the old alternator stator and rotor. But it is not enough to exchange the regulator/rectifier only. One might consider to use the 12V type from the 750 roundcase or 860 square case models, which look absolutely identical as the 6V single R-Rs and invites you to connect it in the same manner as the 6V type. Using one of these R-Rs, you might achieve 12 V output voltage, but only at very high revs, and with low power. The right solution ist to modify the 6V R-R with some special electronic devices, which convert it into a 12V versiojn, or use a modern so called "shunt regulator". These are available on ebay, from Chinese manufacturers, for less than 20$. But both solutions require the appropriate modification of the alternator's wiring scheme.

Hans

dlearl476
Posts: 25
Joined: Thu Feb 28, 2019 12:28 am

Re: '68 350 Scrambler-12V conversion questions

Postby dlearl476 » Fri Oct 18, 2019 1:01 am

Thanks, Hans.

Yes indeed, it’s a Morotrans alternator I sourced from Phil back when that’s all that was available.

I’m sure it will be fine for my application. And Phil said the same, just insulate the blue wire.

dlearl476
Posts: 25
Joined: Thu Feb 28, 2019 12:28 am

Re: '68 350 Scrambler-12V conversion questions

Postby dlearl476 » Wed Oct 23, 2019 1:52 pm

So, I’ve hit a brick wall. My points aren’t opening. Well, the are, physically, but the test light never goes out whether they’re open or closed.

Figured I must have broken the phenolic isolator on the points, so I put a new set on. Same thing.

Long story short: It’s my coil. When I have the coil hooked up, constant power through the points, open or closed. Disconnect the coil lead and it works as standard.

Any ideas?

ranton_rambler
Posts: 439
Joined: Sun Jun 04, 2017 11:33 am
Location: Stafford UK

Re: '68 350 Scrambler-12V conversion questions

Postby ranton_rambler » Wed Oct 23, 2019 6:35 pm

Have you got a diagram of how it’s wired up?

Jordan
Posts: 1380
Joined: Fri Dec 24, 2010 11:29 am

Re: '68 350 Scrambler-12V conversion questions

Postby Jordan » Wed Oct 23, 2019 9:57 pm

Try disconnecting the condensor, in case it's shorted internally.
Got a spare coil to try? One from an old car should work.

dlearl476
Posts: 25
Joined: Thu Feb 28, 2019 12:28 am

Re: '68 350 Scrambler-12V conversion questions

Postby dlearl476 » Thu Oct 24, 2019 9:12 am

ranton_rambler wrote:Have you got a diagram of how it’s wired up?

It’s wired per the ‘68 Wiring diagram. Save for one loose ground that I found today before I put it away. I’m moving on to another project until my new coil arrives. We’ll see what happens with a good coil.

ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: '68 350 Scrambler-12V conversion questions

Postby ducwiz » Thu Oct 24, 2019 5:57 pm

dlearl476,

So, I’ve hit a brick wall. My points aren’t opening. Well, the are, physically, but the test light never goes out whether they’re open or closed.


This conclusion imho is wrong. The test light is usually connected in parallel to the points and capacitor, and you did so. Hence, it is lit when the points are open, goes out when they close. This means also, that your capacitor has no internal short.
Seems there is no connection to ground.

Hans


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