Electrical issue

I suppose that if the load was, say a constant 19A, the fuse shouldn't blow but there might be enough heat generated over time to melt a plastic holder that was not designed to handle that. Whatever happened to good old Bakelite? Of course, if the load is that high in normal operation, something is seriously wrong electrically. A clamp-on Ammeter would be helpful to monitor the load while the bike is operating.

@Triton Thrasher here we go again...
...and yet again, another post that I’m checking out on before the bitching starts.
Why not try and help people rather than bitching and sniping all the time?

@WEM if there is anything I can do to help, drop me a message directly and I’ll do whatever I can.
But in this thread, I’ll leave you in everyone else’s capable hands!

Hopefully, I think I might have eliminated the reg/rec. Performed the test as per instructions Gtiller graciously provided with the following results:

Test No. Podtronics OEM (I kept the original rectifier ca. 1974!)
1. 550. 468
2. 0. 0
3. 539. 488
4. 0. 0
5. 542. 463
6. 0. 0
7. 535. 465
8. 0. 0

I'm not sure what units these numbers represent, but they are pretty consistent across the two individual devices which I believe is the important factor.

I agree that the fact that the fuse holder melts but the fuse doesn't blow is key. It seems entirely counter-intuitive.

Maylar has suggested an ammeter test. Any suggestions regarding which circuits should initially be tested would be appreciated.

Thanks for the all the suggestions. Motorcycle electrics have always been a bit of a dark art to me. No pun intended.

This forum is a great asset.

Ps. One thing I noted yesterday that might factor into what's going on, was that the bike started right up and idled well for quite a while, probably 10 minutes or so with no issues after I replaced the original fuse holder and then ran well on the test rides for about 6 - 8 minutes in total before dying. I wonder if it takes that period of time for whatever is going on to generate enough heat to cause the fuse holder to melt. Whatever is happening doesn't seem to be instantaneous.

Just a quick follow up...from an examination of the second fuse holder, it looks like the fuse holder melts and allows the fuse to lose contact with the end contacts in the fuse holder allowing the circuit to be broken before the fuse itself blows?

I think you are going to have to monitor the amperage. If you use a standard multimeter, be sure to check to see the maximum current rating it can handle in the amps configuration. Based on what's happening with your Norton, if it's not at least 20 A at system voltage, then you could fry the MM or, hopefully, it's equipped with a fuse that would blow.

To look for a short circuit, I wire a headlight light bulb in place of the fuse. If there’s a short, it lights up. You may find it only lights up with ignition on, or with lights on. That narrows your search down.

If your short circuit is intermittent, that difficult to find! You can try waggling the handlebar and pulling the wiring harness around and see if the bulb lights.

To find a short, divide and conquer. Divide the system by disconnecting a branch circuit ( example: ignition off as TT suggests), or physically removing a wire from a terminal where the branch circuit obtains its power. When you find the offensive branch, follow it down by dividing the branch until you conquer.

Slick

WEM said:

I agree that the fact that the fuse holder melts but the fuse doesn't blow is key. It seems entirely counter-intuitive.

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For the life of me I can't think of any electrical device on a bike that would behave that way.

Maylar has suggested an ammeter test. Any suggestions regarding which circuits should initially be tested would be appreciated.

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The obvious place would be inline with the main fuse. But prior to that I'd take an ohmmeter between the ignition switch side of the fuse and ground (fuse removed). With the key on and no lights see what's there. A "15 amp" short will be less than an ohm resistance. Wiggle things about, especially handlebar switches, looking for a change. If you get 3 ohms or more it'll be safe to put a 10 amp ammeter inline with the fuse. Most meters with a 10 amp scale have an internal fuse, so you should be OK to test.

texasSlick said:

To find a short, divide and conquer. Divide the system by disconnecting a branch circuit ( example: ignition off as TT suggests), or physically removing a wire from a terminal where the branch circuit obtains its power. When you find the offensive branch, follow it down by dividing the branch until you conquer.

Slick

Click to expand...

This is accurate advice.
The down side, the snap/bullet connecters that despite best efforts pull themselves off the wire. Be careful.

texasSlick said:

To find a short, divide and conquer. Divide the system by disconnecting a branch circuit ( example: ignition off as TT suggests), or physically removing a wire from a terminal where the branch circuit obtains its power. When you find the offensive branch, follow it down by dividing the branch until you conquer.

Slick

Click to expand...

Thanks. I can usually find a short but I was having difficulty writing a description of what I’d do.

concours said:

This is accurate advice.
The down side, the snap/bullet connecters that despite best efforts pull themselves off the wire. Be careful.

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Ah, yes, the old "pull the wire out of the bullet" problem.

Perhaps this deserves a new thread, but I'll hazard a thread detour here.

Should you manage to pull the bullet without damage, apply a little anti-oxidation grease when reassembling. Use anti-ox on ground connections also.

Should you need new bullets, find a source here:

or here:

Note: Lucas bullets are 0.188" dia, many others are 0.180" dia and not interchangeable.

Slick

L.A.B. said:

A loose 'ground' there is unlikely to be the cause a fuse blowing, also, the wire connection to the headlamp shell is not a headlamp 'ground' but a return connection (to harness red) for the front direction indicators.



That red wire is also not a 'ground' but a return for the Zener diode so if the Zener isn't fitted then the red wire is redundant.

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So just to sure if you don’t have a zener what should you do with the red wire. I fixed mine to the back of the Z plate with no problems as I assumed (incorrectly) it was a ground (+)

Steves said:

So just to sure if you don’t have a zener what should you do with the red wire. I fixed mine to the back of the Z plate with no problems as I assumed (incorrectly) it was a ground (+)

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It can either be left attached to the Z plate or taped back to the harness, as without the Zener the red return wire has no further purpose as the red wire is the ground, not the item that it is attached to (Z plate) because the system of red wires running through the harness is 'ground' and not the 'frame'.

Steves said:

So just to sure if you don’t have a zener what should you do with the red wire. I fixed mine to the back of the Z plate with no problems as I assumed (incorrectly) it was a ground (+)

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It is a sort of frame ground and certainly could stay there. The z-plate is bolted to the frame, though precariously through painted surfaces. But the engine is suspended on rubber, so a frame ground means nothing.

The Commando does not rely on frame ground (that I know of) except for the old points condenser pack on the coil bracket, and that had its own wire.

maylar said:

The z-plate is bolted to the frame, though precariously through painted surfaces.

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Which is why the Zener has its own 'ground' wire.

maylar said:

The Commando does not rely on frame ground (that I know of) except for the old points condenser pack on the coil bracket, and that had its own wire.

Click to expand...

The rear direction indicators make partial use of the frame for their return where the ('73-on) L917 tail lamp is fitted as it doesn't have a ground connection between the bulb holder and the lamp bracket although the earlier L679 lamp does.

Make sure the glass fuse is a 35amp fast nlow not slow blow. If usung standard Buss types, 15 or 20 amp.

Thanks again for the excellent advice/ideas. I have a new piece of info after today's fiddling around. I installed a new plastic fuse holder with a 20 amp SFE fuse and the bike again started up and ran perfectly for about 15 minutes or so before I turned it off. Idle was steady around 1000rpm. I didn't go for a test ride as I wasn't looking forward to probably having to push the bike home so the bike didn't get up to full operating temp. I took the opportunity while bike was running to test alternator output. With bike off, multimeter read 12.20 v on battery. Turned ignition on and reading dropped to 11.93 v. Started bike and reading at idle was 11.93 v. The interesting thing occurred when engine was revved to 4000 rpm. At 4000 rpm, reading on battery was 11.99 v. It seems like alternator is producing hardly any current. I mentioned earlier that, prior to this whole episode of the bike melting fuse holders, that the red WLA indicator light would come on when the ignition was switched to on position but would go off as soon as bike started, no matter if idle rpm's were below 1000 rpm. After the fuse holder incident, the WLA light stays on after start until rpm's reach over 1000 rpm. I know this is supposed to be how the WLA works but the interesting thing is this is a new development on this bike which only started after first fuse holder melted. I'm not sure if the dodgy alternator might be the cause of the melting fuse holder problem, a result of the fuse holder problem or unrelated at all.

Well, it could be that the alternator is working perfectly and the load that is causing the fuse holder to melt is exceeding the charging system's ability to charge the battery. As suggested, do an amp draw test!


"The Commando does not rely on frame ground (that I know of) except for the old points condenser pack on the coil bracket, and that had its own wire."

Although I agree that one can correctly say that the commando does not rely on a "frame ground," I think it is misleading because the OEM wiring harness attaches to the head steady, NOT to the engine. Therefore, it is more like a frame ground than anything else. The points system was grounded to the engine, as are some aftermarket E-ignitions and, of course, the spark plugs are grounded to the engine. A poor ground to the engine can produce all sorts of curious problems so the practice of extending the OEM ground directly to a bolt on the engine is a more positive (NPI!) method.

MexicoMike said:

Although I agree that one can correctly say that the commando does not rely on a "frame ground," I think it is misleading because the OEM wiring harness attaches to the head steady, NOT to the engine. Therefore, it is more like a frame ground than anything else.

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Not sure I follow, as the head steady is isolated from the frame by the rubber mounts so yes, it's the engine 'ground' (except for Mk3 or where the Mk3 suspensory spring is fitted) therefore I can't see how it can be a 'frame' ground.

Well, my issue with the OEM ground is that it's not directly attached to the engine. In theory, I agree that the ground on the Norton is OK...when new. But since the engine is grounded through the headsteady which is then connected through a series of plates/bolts to the engine, each of those "connections" is subject to corrosion. A direct connection to the engine reduces the likelihood of corrosion/circuit degradation that increases with the more connections there are in a circuit. Plus, it's very easy to do and only does good things!