175TS Electrical Puzzles - Please Help!

[Samurai]

Hi Guys,
I’m in need of some advice from those of you who are almost certainly more skilled in the ‘black art’ of ‘electrickery’ than I am!

First I must apologise for the long post, but I think you may need a little background which may or may not shed some light on the issues. I have been carrying out a full restoration of an Italian made 175TS narrowcase, using the original battery ignition system. 1959 model according to the dating certificate from Mick Walker.

The engine has been fully rebuilt and is now running fine. I recreated the original wiring loom from scratch and ensured that it matches up with the relevant wiring diagram and advice provided by Ventoduo, Ducwiz and Hans in this thread: http://www.motoscrubs.com/forum/viewtopic.php?f=3&t=2575&p=19182#p19182.

The generator/alternator has also been completely refurbished/rewound by a well know classic bike electrical specialist here in the UK, Rex’s Speedshop and was supplied back with the correct coloured wiring.

Now to the problems two electrical problems which may be linked, or perhaps just coincidental?

1. Despite repeated checking of every connection and careful comparison with the wiring diagram, by both myself and my son (who is an electrician by trade, although not an auto-specialist), we cannot get the headlamp bulb to light. However, all other lights, horn and electrics appear to work just fine (see issue 2 though?)

We know that there is power to the bulb holder connections and that the bulb itself will light if connected directly to the battery. The issue would appear to be something to do with a bad earth, although I have also tried running a ‘fly lead’ earth from the bulb holder negative to the frame with no effect?

2. Having now got the engine running, I tested the voltage across the battery terminals with it at a fast idle (I would guess around 1500 – 1800 rpm). Being ‘electrically naïve’ and only used to modern 12v systems, I was surprised to see the voltage across the 6v battery terminals fluctuating between 12.5 and 14 volts and rising to about 15.5 volts when the engine speed was increased further. These reading are what I would have expected from a 12v system and I’m concerned that the sealed battery I’m running will overcharge, with potentially disastrous consequences. What sort of reading would be normal for a 6v system under these circumstances?

From the information I’ve gleaned from my previous post, I understand that these early Ducati electrical systems don’t use a regulator (just the Westinghouse rectifier), relying instead on just providing the minimum juice required for the demand, by switching in the lighting coil only when required.

Is it possible that the alternator has been rewound or wired-up incorrectly and I’ve therefore inadvertently transposed connections at the frame connector block? Might this also be a reason why the headlamp is not working either?

Any help and advice would be really appreciated as I’ve run out of electrical talent! It’s been a long road getting this far, the bike has fought me a lot of the way and it’s really frustrating to have these problems now that the end is nearly in sight, particularly when it revolves around the area I’m least comfortable with

[Bevel bob]

Hi, If it is a battery bike I would expect the HL to work without the motor running ,but I have no info on the 175Ts so I may be wrong! If you have had powdercoating done then it is a great insulator!. That voltage will cook the battery. If you have rewired the alternator using conventional logic then that may be the problem. Ducatis are just weird and As i could not understand it I just removed the earth wires on the coils and connected together and fitted a modern rec/regulator and changed coil/hooter/bulbs and went 12v. No problem since.Someone who knows what they are doing(not me!) will post soon.

[Samurai]

Thanks for the reply Bob, glad I'm not the only one to be baffled by Ducati electrics

The bike should really be about as simple as it can get but the Italians appear to think otherwise

When you say you connected the earth wires to the coil together when converting to 12v, what did you connect the earth wire leading to the points with exactly and why?

Just interested in case I eventually decide to go down that road, although my preference is to try and keep the bike as stock as possible.

[Bevel bob]

My bike was the later 250 with the 60 watt Alternator and "normal" HA HA!, 6 v ignition but with the usual crazy Ducati charging system. Inside the alternator two of the stator coil wires were connected to earth (usual for Ducati but not anywhere else!) .These I disconnected from earth and linked them together (putting the coils in series,I think!) .this is now capable to run a 12 v system if a modern rectifier/regulator is used. Other items had to be changed to use 12v. Mind you I still have no idea what goes on in the headlight shell.(And Don't want to know).

[Samurai]

Just thought I'd update this post to let you know that I've finally got the headlamp to work.

After working my way through the power supply from the battery to the main headlamp switch with a multimeter, I found that one of the 'forks' that makes the conections on the circuit board, was only making a partial connection to the 'soldered blob'. Some voltage was getting across to the headlamp circuit, but not enough to power the bulb!

Small victories and another step closer to getting this bike back on the road and off to Italy

[Samurai]

Further update on the rollercoaster ride of electrical problems!

Having celebrated what I though was a minor victory, upon putting the headlamp shell back together the main fuse started to blow again. After another couple of hours poring over the wiring diagram and methodically trobleshooting, my son and I traced the potential source down to the reproduction horn casing that I fitted as part of the restoration (the original had gone brittle and was disintigrating).

We swapped the metal casing back to the original just for the hell of it, even though it is such a simple component and looked identical in construction. Damn thing worked fine and no blown fuses. Repro casing back on and fuse blows!

My electrician son can't understand why Ducati saw fit to ground the metal casing through the handlebar screws AND provide a second ground wide to operate the horn. All we can assume is that the horn button rivet has done tiny insulating washer between it and the casing, as otherwise the while casing and frame would be live all the time - hence the constantly blowing fuses on that circuit!

For some reason the reproduction part can't have this insulating washer or it has failed somehow. Still a dumb design anyway