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Original Post (Thread Starter)
by maxsettings
maxsettings
I have a 1970 Thunderbolt. Yesterday I was riding and lost all power, bike shut off. It appears to be an electrical issue:

If I turn the ignition on the headlamp and brake light no longer light up. Bike currently doesn't have indicator lights. And no longer can start bike.

Electric work is not my strong suit. Bike has Tympanium regulator installed and is still positive earth. Using a mulitmeter and testing light I have tested all the wiring I can get to, all wires gave reading except two yellow wires coming from the regulator. The stator appears to be good using the multimeter for testing.

My only idea at this point is perhaps somewhere in the wire harness theres a short, split wire but haven't been able to find anything.

Looking for suggestions before I start replacing the entire electrical system.

Also note battery is brand new and maintaining 12.5-12.8v.

Thank you!
Liked Replies
by Mark Z
Mark Z
I don't think there's any dispute over the fact that the engine must be electrically connected to the "ground", "battery return", or, in a positive ground system, battery (+).

Now, whether it's necessary or not, and whether or not you run a wire from the engine to the battery, the engine WILL be electrically connected to the frame. In fact, it would be difficult to insulate it from the frame. And to the frame are connected many other metal parts, fenders, fork yokes, handlebar, etc. In fact it's necessary for the handlebar to be "grounded" if you have a one-wire horn switch.

In order to avoid having many wires on the battery (+) terminal, or having many inline splices or connectors, it's convenient to have a "ground post" - where? Well, on the frame of course.

So, like it or not, the frame and most of the metal parts on the bike will be electrically connected to "battery return", and if any supply-carrying wire touches any of these "grounded" parts without first going through an appliance, a short circuit will occur and blow the fuse (or burn something if there's no fuse in the circuit).

It's also convenient to use the term "ground" (or "earth" if you prefer), just as it's convenient to use the ground symbol in a schematic diagram, so you don't have to draw all the lines that connect to the same point. We know that "ground" means a return to the battery; we've heard it enough times, so let it go.
1 member likes this
by Stuart
Stuart
Hi Mark,
Originally Posted by Mark Z
the engine WILL be electrically connected to the frame. In fact, it would be difficult to insulate it from the frame.
Actually, it's quite easy in practice - well-painted or -powder-coated frame, carefully-installed engine, the engine is often insulated from the frame. I wasn't the first to advise a wire from the engine; I copied the tip from John Healy, working on 1970's Britbikes electrics, I noticed Lucas did it, and there were random electrical problems when the wire between engine and battery +ve was missing.

Originally Posted by Mark Z
In order to avoid having many wires on the battery (+) terminal, or having many inline splices or connectors, it's convenient to have a "ground post" - where? Well, on the frame of course.
Uh-uh, no "of course"; OIF and 1970's triples (? Triumph), Lucas soldered the ends of component Red wires to a washer, that washer attached to an engine component. If the wire from the washer to battery +ve was forgotten, because other component return wires are by definition attached to the engine exacerbates the aforementioned random electrical problems.

Careful assembly, whether or not any non-electric cycle part is connected is irrelevant.

Also, I've never used a "ground post", frame or engine. The vast majority of electrical components are either at the front of the bike or in the middle, the latter including the battery; I did my first rewire long before there was an internet; I found connecting the components around the headlamp to one snap connector, the components under the seat to another snap connector and connecting the snap connectors together with one wire used the least wire, far less even than Lucas used connecting components to a "ground post".

Originally Posted by Mark Z
And to the frame are connected many other metal parts, fenders, fork yokes, handlebar, etc. In fact it's necessary for the handlebar to be "grounded" if you have a one-wire horn switch.
So, like it or not, the frame and most of the metal parts on the bike will be electrically connected to "battery return",
Unfortunately, relying on that fails in reality. The horn doesn't work because, while the horn button might be "grounded" to the handlebar and the handlebar to the yoke, the forks can be insulated from the frame by something as simple as well-greased steering bearings ... facepalm Simple and ime long-term reliable is to connect a wire from the horn button or the handlebars into an existing Red wires' snap connector inside the headlamp shell or under the tank.

The tail/stop bulb is another component that relied for many years on metal-to-metal contact between several random cycle parts, and fails either when dirt and corrosion get between the metal components or better-painted or -powder-coated components are fitted. Lucas eventually 'admitted defeat' by fitting rear lamps with the third, return, wire from about mid-'71-ish afaict.

Otoh, Lucas never fitted their turn signals with return wires; old-Britbike internet forums are littered with posts both by people who bought Triumphs and BSA's new and removed the turn signals soon after because they stopped working, and/or they can't get them to work now; fixing that by adding return wires was so common long before there was an internet that I do it and advise it as a matter of course.

Unlike Lucas, the Japanese bike manufacturers did rely on "most of the metal parts on the bike will be electrically connected to "battery return""; again long before there was an internet, adding a Lucas-style supply wires network connected to battery -ve solved so many apparently-random electrical problems on high-mileage Japanese bikes it's something I'd do as matter of course.

Originally Posted by Mark Z
It's also convenient to use the term "ground" (or "earth" if you prefer),
Like any jargon word, it's fine if everyone in the conversation has exactly the same understanding of the jargon. Unfortunately, reality shows different people don't of "ground"/"earth" - e.g. recently, the OP of the "Digital Speedometer Problem" thread on British Motorcycles In General? While there are many, many similar examples, another I remember particularly was on TriumphRat - a contributor posted he'd connected his 'negative ground' truck to his 'positive ground' Triumph ... luckily, his Triumph's battery was shagged so he only put about 17 or 18 Volts across his Triumph's electrics, which luckily didn't have any electronic components ...

That's the reason I try to avoid using "ground"/"earth", nothing to do with sub-atomic particles, "supply" and "return" are a convenient hook and, more importantly, aren't jargon.

Originally Posted by Mark Z
We know that "ground" means a return to the battery;
BSA's, yes; Triumphs, not always ...

Regards,
1 member likes this
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