Which wire

[oldchuffer]

I need to make some fresh cables to the rear light cluster but i'm not sure which rating i will need. I saw the attached on the Vehicle Wiring Products website but which should i get?

[sye]

It's only around 3A for the rear light cluster.

[McCabe-Thiele (Ted)]

Even less if you fit an LED - I would go for 3amp in stranded copper.

[Oddjob]

You mean the 3 wire small harness? I should have a decent spare if you are. Just postage for a fellow old chuffer. I'll have a look, going into the loft now to check on something else so I'll see if I can find one.

[oldchuffer]

I've checked the loom again (its off the bike completely) and i can see a plastic shroud which has the brown, green/yellow, light blue and orange (for the winkers) and several greens (earths?) The rear light has two, the green/yellow & brown but only about 4 inches of wire. Where abouts does this shroud sit?

[McCabe-Thiele (Ted)]

The earths were originally attached to the brackets that hold the winker. Mine were long rotted away so I connected fresh earth wires from the lamp bases to the loom.
If we're talking about the same shroud it sits just under the seat peeking  above the plastic rear mudguard.

[oldchuffer]

Thanks Ted, i've just seen you have asked this before, complete with a pic. Ignore my PM.

[Oddjob]

Rear light normally has 3 wires, brown, green/yellow and a green for an earth to the rear light itself as it's normally rubber mounted so doesn't have a good earth against the body. The earth wire normally has a spade connector on it whilst the other 2 are normal bullet connectors.

[Lobo]

Personally, I’d be trying to keep the wiring as close to standard as possible - it simply avoids headaches down the track. It also allows you / any subsequent owner to revert to OEM equipment without any worries at any time.

If I remember correctly, the CB400 has 3 fuses, inc a 7A fuse on the Taillight circuit. DON’T use 3A wire into this circuit, as if there is a short your new wire will begin to smoulder / smell / spoil your day long before the fuse blows. Ie use wire > than the fuse in said circuit. (It doesn’t matter if you use LEDS or not… a short circuit will basically connect the live wire directly to earth… and you need the fuse to blow FIRST)
You might instead change the fuse in question to a 3A …. if so make sure you know what else there is on that circuit and whether this is a viable option - I can’t remember.

Finally those new connections. ALWAYS put the shrouded Female on the supply (battery) side of the connections, and the bullet towards the component (ie bulb). In this way, if a connector undoes, the jiggling (live) female side will not short to the frame / Earth.

[McCabe-Thiele (Ted)]

Personally, I’d be trying to keep the wiring as close to standard as possible - it simply avoids headaches down the track. It also allows you / any subsequent owner to revert to OEM equipment without any worries at any time.

If I remember correctly, the CB400 has 3 fuses, inc a 7A fuse on the Taillight circuit. DON’T use 3A wire into this circuit, as if there is a short your new wire will begin to smoulder / smell / spoil your day long before the fuse blows. Ie use wire > than the fuse in said circuit. (It doesn’t matter if you use LEDS or not… a short circuit will basically connect the live wire directly to earth… and you need the fuse to blow FIRST)
You might instead change the fuse in question to a 3A …. if so make sure you know what else there is on that circuit and whether this is a viable option - I can’t remember.

Finally those new connections. ALWAYS put the shrouded Female on the supply (battery) side of the connections, and the bullet towards the component (ie bulb). In this way, if a connector undoes, the jiggling (live) female side will not short to the frame / Earth.

Interesting logic you have put forwards never looked at it like that - presumably the fuse will blow when the current exceeds the sum of all the items on the circuit plus you would also allow extra to avoid a voltage drop down a long wire route. I generally find that the wire I have in stock  is never less than 1.5 mm so I tend to slightly over design and go for 2.0mm but then you can have a new mini loom that will not fit through an apperature e.g. hole in rear mudguard.. Presumably the tail light fuse would include F & R light, instrument lights & stop lamp.

[Oddjob]

Never put "jiggling" and "female" in the same sentence Lobo, it conjures up too many images. 

[McCabe-Thiele (Ted)]

Never put "jiggling" and "female" in the same sentence Lobo, it conjures up too many images. 

jiggy-jiggy has a lot to answer for internationally.

[Lobo]

Jiggy-jiggy….. ah the memories 😂.

Yep Ted, the summation of all currents in the circuit will go through the fuse, and blow it if greater than its rating. Nevertheless, if a full-on Earth short occurs in the tail lamp (as in this thread) wiring, then this new wire will have to locally cope with all that current.

Ergo, you don’t want to install wiring anywhere in the circuit less than the rated fuse value. (and if insisting on smaller value wires due bulkheads / apertures etc consider fitting an inline smaller fuse within that section)

[McCabe-Thiele (Ted)]

Jiggy-jiggy….. ah the memories 😂.

Yep Ted, the summation of all currents in the circuit will go through the fuse, and blow it if greater than its rating. Nevertheless, if a full-on Earth short occurs in the tail lamp (as in this thread) wiring, then this new wire will have to locally cope with all that current.

Ergo, you don’t want to install wiring anywhere in the circuit less than the rated fuse value. (and if insisting on smaller value wires due bulkheads / apertures etc consider fitting an inline smaller fuse within that section)

I've learnt a lot about wiring - presumably they do not follow the same rules with small stuff like clock illumination due to cost & low current load on that part of the lighting loom circuit.

When my mind is wandering thinking I have grasped a concept I then wonder why a fuse does not light up like a bulb - maybe it does just before it blows!

[sye]

I then wonder why a fuse does not light up like a bulb - maybe it does just before it blows!

The wire used in fuses has very low melting points, usually tin, lead or zinc. They do light up just before they blow too.