Ground wires

[kaysystems]

It has been over 40 years since I disassembled my Mark 3 (battery version). The wiring had been modified and was a bit unreliable.

How is everything grounded?
There should be a wire from the battery to the regulator, and the frame. Where was the factory ground?
How are the front and rear lights grounded?
How is the engine grounded?

I'm assuming the factory hoped that parts bolted together would provide grounding

Thanks

David

[JimF]

Yes, the engine and frame provide the intended electrical system grounding. The negative battery wire is connected at a fastener to the frame. The engine is at ground potential by virtue of its mounting bolts.

I believe the headlight bucket and taillight both utilize ground wires that will connect to a fastener that is securely threaded into the frame, probably because the paint on the headlight bucket and the taillight bracket acts an electrical insulator.

That being said, is your Mark 3 a narrow case? Is there a toggle switch mounted on the top of the taillight bracket? If so, the ignition system's ground is made through the brake pedal switch (whose quiescent state is closed) when the rear brake is not being used.

Pushing on the brake switch opens the ground circuit and a wire coming off the brake switch diverts the ignition system's amperage through the brake light bulb, thus using the current (amperage) of the ignition system to light the brake light bulb.

[kaysystems]

The easy one - yes it is narrowcast, but a European model with 6v battery and regulator, so no switch on the rear light.

If everything is grounded by virtue of contact, then I need to remove paint from a few places at the bolt holes (fenders, engine mounts etc)?

David

[JimF]

I wouldn't bother to remove paint. The threads of the fasteners will be 'neck deep' in the tapped holes of the frame. Where you currently have paint is to me an indication that the factory did not see the need to remove paint to enhance electrical contact.

If you are still concerned, I would suggest removing paint that will be hidden underneath the head of the fastener to preserve as much of the "cosmetic' appearance as possible, and also to prevent rust.

[A.I.M]

Hi David,
My Scrambler, 6V electrics, has earth wires fitted to (1) the headlight shell; (2) the frame, near the battery, and (3) an extra, non-standard, engine earth which I added to the clutch cable bracket, just behind the cylinder. That may not be the best position for it; with some forward planning and the right fittings it could go to a more secure point on the engine, but it works fine for me.
Cheers,
Al

[Jordan]

I saw a regulator taken from a 1980's Honda (I think it was).
It had a brass strap from the earth connector to one of its frame mounting bolts.
It also had an earth wire with a bullet connector, evidently for some other earth location.
"Belt and braces" for reliability.

[blethermaskite]

After years of dodgy Ducati electrics I have put ground connections on everything, I particularly recommend putting a permanent and secure ground from the engine to the frame, I use a custom head stud washer with a 'wing tab' for wire fitment, I also believe you should use a main dedicated 'ground post somewhere on the frame (bare metal fixing) and run all the ground wires to this one point (including the battery). This might sound a bit like overkill but it just means everything will work ........well until those bits fall off from the vibration! This is the other reason for ground wires ..... they help catch's the bits that fall off .
Cheers George

[themoudie]

Aye David,

I concur with George's (blethermaskite) comments. Put the multi-coloured spaghetti in the bin and make a new loom, using modern materials.

On my '74 450 MKIII widecase machine, I have a central earth point on the frame beneath the seat, with earth leads all wired to this point, as is the engine and a lead from the headlamp/lighting circuitry. Unlike Ducati's reliance on an earth via the headstock ball bearings!

I also use "Thinwall single core cable and Japanese "standard" 3.9mm bullet connectors.

Good luck, with the knitting, BillR

[ranton_rambler]

Same for me - my 175TS had a mish-mash of bits and as I was converting to 12V and using an Electrex reg-rec I made a new loom from scratch with earth leads for everything and a modern fuse box under the seat. I would have to look, but I think my battery negative goes to one of the engine mount bolts so both frame and engine are at a common point.

Regarding paint, in my day job we often had problems getting good earths onto powder-coated chassis parts. One solution is to use hardened star washers under the bolt heads which bite through the coating to the steel beneath.

Ian