Request for assistance - 1979 900 Replica - electrical probs

[Blacklightning]

Afternoon All,

I'm in the final stages of re-building number 146, a 1979 Ducati 900 Replica.

Most all has gone according to plan on the restoration so far.

I have now re-installed the wiring loom and have some electrical problems:

The handlebar left hand switch doesn't appear to control anything except the indicators.

No horn
No lights

When I put the indicators on, rear ones work perfectly - the front ones left and right come on together and blink - even though there is only one wire going to each, black and white to one and green and white to the other - from the headlamp shell loom - just like the wiring diagram. Can't be the flasher realy surely as the rear ones flash brilliantly and individually - so there must be a short somewhere?

The handlebar switch appears to have an earth running into it, I've spurred a cable off that connector to the frame just to double check connection and OK.

The ignition switch and cluster appears to be working - parking light comes on and ignition light (neutral) comes on in the other position. Indicator indicator lights flash one at a time when the indicators are switched on even though the front indicators blink together.

The ignition system appears to work - nice healthy spark in each cylinder (so that's something)

The front brake light switch works

The rear brake light switch works

So, it appears the main bulb in the headlamp can't be activated and the handlebar switch doesnt't appear to control lights or horn.

My bike has a slightly different loom than the wiring diagram I have - I have two bulbs in each of the speedo and rev counter whereas the wiring diagram only shows one. There are then a pair of live leads coming from each of the speedo and the rev counter into the wiring loom.

i guess it does not matter which of the four leads from the loom go to which of the four bulbs in the speedo/rev counter - I can't vouch that they are all in the original place but I'm deducing that they are simply four live leads, neutral being back through the frame so I can't see it causing an issue.

Work done: for info the bike has been completely stripped. The wiring loom has had all the connectors cleaned and polished with a dremel (that took a while) and the handlebar switch has been dissassembled and restored. I rebuilt it using a load of photos I took.

Ditto headlamp has been restored. There are two wires joined together coming off the back of the main bulb assembly that have female spade connectors on them, and the side light assembly has a male spade so I've connected them - the wiring diagram shows this I think.

I've been carefull and put the loom back together using photos I took, I will go over it all again but I thnk I have got it right. The connectors have all been put together with connector lube.

I don't have any spare connections in the loom that I can see.

The fuses are all intact and show continuity.

I kinda hoped that a more experienced forum member will be able to point me to the source of my errors?

Any advice gratefully received.

Regards

Stuart

[wdietz186]

Your symptoms sound like a grounding problem. Both of the front indicators flashing means the ground on one side is open and is getting its ground through the other side by way of the flasher. IIRC the headlight bucket needs to be positively grounded as the lamp and horn ground wires attach to the shell.Most of the time the bolts do this but if the paint is thick it may not be enough. Try running a wire from the shell to the frame,making sure the wire is contacting bare metal at both ends. Star washers between the terminal and frame will insure positive contact for a long time.In the same vein,many charging issues stem from poor contact between the cases and frame and a dedicated ground wire is often the cure for a weak charging system[except for 750GTs and early 860s,they are just inherently weak].

[Blacklightning]

Many thanks - will try and let you know.

S

[Blacklightning]

OK, so that has fixed the indicators - many thanks indeed.

I've run an earth from the headlamp shell and the indicators are now working fine.

But no joy with the lights and the left handlebar switch.

I have checked that I have assembld it correctly from photos etc. That seems fine.

But no horn, no light control and so I am deducing that I need to trace that back into the wiring harness and check the connector.

I have run a separate earth for the handlebar switch but doesn't seem to make any difference.

Any further thoughts much appreciated?

Stuart

[wdietz186]

Have you checked for voltage at the headlight and horn? Is the bulb burnt out? Any blown or loose fuses? Do you have voltage to the switch? You could have a problem in the connector[s] that the switch plugs into. You should trace the the circuit from the battery to the lamp and see where the voltage stops. Same applies to the horn.All the wiring looks kind of intimidating but it is simple once you isolate the wires for the circuit you are dealing with.

[Blacklightning]

Thanks for that, that is very helpful - wiring not my forte....thanks for the encouragement....I will break it down into steps as you suggest and try to sort it out that way.

Keep you posted.

S

[Blacklightning]

OK, problems sorted - I feel a little stupid but it's my first bike restoration and if this is the worst of my errors then that's not too bad. I'll own up so hopefully someone else can learn from my mistake - and also others can have a laugh....and laughing is good for you.... <> <> <> <>

So, I spent many happy hours using a dremel to polish every spade, bullet and block connector on the wiring loom to restore it and get it ready to re-fit. I polished every terminal on the fuse block too - the wiring loom was a thing of beauty to behold.

Then I put it all back together again with connector lube, and having checked the fuses were complete, slotted then back in.

BUT I didn't clean or polish the bullet ends of the fuses. Yes, you've guessed it - no live power to the handlebar switch, nothing coming off the fuse box.....took out the fuse, polished the bullet ends with emery paper - everything works just like it should.

Oh dear oh dear oh dear - I feel foolish.

Anyway, great news is that it's done, it's fixed and if I had only done it first time then the wiring would have worked first time and I'd have been really chuffed.

If only I could find a way of posting pictures without a hosting service I could show you the fruits of my efforts. I've tried shrinking a file and posting it direct but then got told it was out of size (dimension).

Anyway - this evening I drilled the holes for the four fairing mounting screws around the headlamp and that completed the original one piece fairing. Then drilled a new screen to fit and fitted edging rubber.

So, a short list of small jobs to do to finish...nothing major, nothing complex and nothing more than a couple of hours or so.

She's done....ready to fire up. Bought in October 2011 and now close to ready to return to the road.....in time to be run in and then taken to the Isle of Man Manx Grand Prix in August where she is booked on the Closed Road Parade.

Just about ready to be taken out and let people appraise her....spot the 5 stainless bolts that I have on her (ouch, must fix that) and let me know what else I have done which isn't "as original"....lol......

Thanks to everyone for their help along the way. Let's hope she starts - but as Gtec did the engine, JRS the carbs I'm feeling pretty confident

Regards

Stuart

[wdietz186]

Stuart, We all know these things because we've all been in the same situation.I forgot to mention how crappy the origional fusebox is.Many of them out there have rubbber bands around the fuses holding the blades tight to the fuses.You can only bend them together so many times before they loosen to the point of poor contact causing high resistance and then they melt

[Craig in France]

Then I put it all back together again with connector lube, and having checked the fuses were complete, slotted then back in.

BUT I didn't clean or polish the bullet ends of the fuses. Yes, you've guessed it - no live power to the handlebar switch, nothing coming off the fuse box.....took out the fuse, polished the bullet ends with emery paper - everything works just like it should.

Oh dear oh dear oh dear - I feel foolish.

You shouldn't . They are Little Darlings, those fuses. As you now know , the ends corrode up. Often, this corrosion is barely perceptible; but it's still enuf to stop things working.

P.s I had just writen you this missive about checking the power supply. So I might just as well post it ... . You'd have found the cause of the problem at Stage 2, I think ...

Horn
Let’s look at the horn first. To make things easier, here’s a cleaned-up version of the wiring diagram.



As you can see, it’s very simple: the feed for the horn comes from fuse F2. It goes to the horn first; then leaves the horn and goes to the handlebar switch where the circuit is completed by being earthed when the horn button is pushed.

So, using a light tester and/or a meter:
1. Is there a feed thru the orange wire that connects to the horn?
2. If no, then check this wire back as far the fuse.
3. If yes, is there a circuit from the other horn connection as far as the horn button in the handlebar switch? This should go via a green wire and pass thru terminal 3 of the 9-pin multi-connector - check this too, nat’.
4. If yes, does the other side of the horn button earth?

[Blacklightning]

Craig,

You are a star, your postings are so helpful - many thanks indeed.

And especially for taking the time to provide such a helpful schematic.

Regards

Stuart

PS - I'm still chuffed that second time around - everything (well everything except the main beam indicator light) works - how cool is that.

I checked the main beam indicator light for continuity when I had installed it, with a meter - so I know it was OK as I put it back together....

Stuart