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Dibnah Offline OP
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Hi all,

My mongrel 650 has a vibration problem, I think it's called character. Following the loss of the tail light unit and number plate several years ago, I mounted the non-standard replacements on anti-vibration bobbin mounts, which have worked well. However, the cables to the tail light fracture perhaps once every 1000 miles. The cabling does not look OEM, possibly 1mm^2, approx 18 SWG. I'm guessing that 1.6mm^2 is standard, approx 17 SWG. Is there a spec for the cabling for 1970s Triumphs, perhaps very flexible?

Similar problem for the cables to the horn, which has some form of anti-vibration mount, possibly OEM or a previous owner.

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Hi,

Originally Posted by Dibnah
cables to the tail light fracture perhaps once every 1000 miles.
Similar problem for the cables to the horn,
The cabling does not look OEM, possibly 1mm^2, approx 18 SWG. I'm guessing that 1.6mm^2 is standard, approx 17 SWG. Is there a spec for the cabling for 1970s Triumphs,
Standard Lucas wiring to parts like rear lamp and horn was 14 strands, each 32SWG - total conductor cross-section was just under 1 sq.mm. If it's been replaced, the widely-available similar metric wire is either 14 strands, each 0.3 mm. dia. or 32 strands, each 0.2 mm. dia., both 1 sq.mm. total conductor cross-section.

Otoh, 1.6 sq.mm. conductor cross-section isn't easily available in multi-strand wire for automotive applications.

The standard Lucas size or the metric replacements above aren't known for suffering vibe damage - the multiple thin strands should resist it. Does your bike look like it has specifically automotive wire? How much loose length is there between component terminals and the nearest restraint - cable tie, taping, etc.?

Hth.

Regards,

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yes or maybe , try looking for some high strand silicone wire .
in the US it would be 14 gauge , in the UK it would probably be 1.5 mm ?
the high strand-count and silicone sheathing
make it extremely flexible ... the colors available may be limited
its like the wire used on most multimeter leads .
it is so flexible it may need extra support between normal spans .
[Linked Image from s.alicdn.com]

The silicone sheathing is also a higher temperature rating than typical pvc .
its what ive used when fixing/replacing the stator wire leads that always go crispy with age

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Where the cables are recurrently fracturing will be a clue.

Cables most often break where they enter a connector, as this is (relatively) a fixed point and the looser length of the cable shakes about it, the angular movement eventually fatiguing the copper strands.

If solder has been used in the vicinity, that can make the cable more vulnerable to fracture, as solder in a cable renders the cable inflexible (its only response to shaking of the wire is to break).
As you appear to have had recurrent breaks, I suspect soldering may be part of the issue.
If soldering is used, it is important to ensure the soldered length is not exposed to any flexing (at the very least a couple of layers of heatshrink extending well beyond the joint).

It is also best that the cables are collected into a sleeve, and the sleeve itself is held by any clamps/grommets.

How the cable is strapped to frame and mudguard assembly is also important, such that there is a little slack to allow for vibration movement, but that such clamping is within an inch or 2 of the terminals (or there is some other support for the cables such as a grommet).

The tail light requires nothing more than conventional 1mm2 cable (14X0.30mm) or 0.5mm2 thinwall (16X0.20mm) cable.
I think the horn would be quite happy with these cables as well.

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Do you have a top engine head steady?

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Dibnah Offline OP
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Thanks for the quick and detailed replies.

One head steady fitted. OIF frame but an earlier engine, 8 stud head.

22 strands of wire for one of the problem cables. Plenty of slack cable adjacent to the fracture points, although the lengh is reducing as I chop bits off!

Fractures occur immediately adjacent to soldered joint or soldered crimp or mechanical crimp. My soldering and mechanical crimping is generally OK for other vehicles (with less high frequency vibration).

I have previously used this supplier for cabling for other vehicles

https://www.eBay.co.uk/itm/RED-TRI-...p;hash=item2a41a54d54:g:o8sAAOSwKfVXDhhL

Edit: link works in preview, but not when posted. UK eBay item number 480449693247 is one example

Edit again: this link to a cabling supplier on UK eBay should be clickable https://preview.tinyurl.com/yxvtrc6v

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Hi,

Originally Posted by Dibnah
Fractures occur immediately adjacent to soldered joint or soldered crimp or mechanical crimp.
Originally Posted by koan58
As you appear to have had recurrent breaks, I suspect soldering may be part of the issue.
+1. Don't solder. At all.

Originally Posted by Dibnah
22 strands of wire for one of the problem cables.
24 strands, = "0.75mm" in the seller's dropdown.

Might be part of the problem. Only ever used the thinner 'thinwall' wires (that's what it is) on one build (the customer bought it). Never again. thumbsdown thumbsdown thumbsdown

What "mechanical crimp" are you using?

Originally Posted by Dibnah
https://www.eBay.co.uk/itm/RED-TRI-...p;hash=item2a41a54d54:g:o8sAAOSwKfVXDhhL

Edit: link works in preview, but not when posted.
Only https://www.eBay.co.uk/itm/RED-TRI-...TIVE-12V-240V-CUT-TO-LENGTH/181489978708 (up to the "?") required. However, still doesn't work even if you use the "Insert link" icon - long-time bug in the Forum software ... frown afaik, the only way for someone else to get the full link is by "Quote"-ing your post the copying 'n' pasting it from the quoted post into a browser tab.

Originally Posted by Dibnah
Edit again: this link to a cabling supplier on UK eBay should be clickable https://preview.tinyurl.com/yxvtrc6v
Also didn't work for me.

Hth.

Regards,

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Dibnah Offline OP
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Thanks Stuart

The cabling purchased from the eBay supplier has been used on another bike, not on my 650, no problem to date on the other bike (modern with minimal vibration).

I've had no major issues with soldered joints / soldered crimps on other vehicles, although none have the same level of high frequency vibration as my 650.

Mechanical crimps are from RS Components, purchased over the years for non-automotive work.

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Dibnah Offline OP
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Tinyurl should be clickable, but not always trusted by other posters

https://tinyurl.com/yxvtrc6v

Tinyurl with preview can generate trust

https://preview.tinyurl.com/yxvtrc6v

Works in preview.

Bizarre. Both links go to tinyurl preview, thus requiring another click on "Proceed to this site"

Last edited by Dibnah; 10/12/20 10:41 am.
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UK-fleabay
https://www.eBay.co.uk/itm/Silicone...4-26-30-AWG-Various-Colours/361296232202

6 colours available , 400 strand [Linked Image from i.ebayimg.com]

Price: £0.99 per meter + postage: £2


the 14ga is rated to 32 amps ... which is overkill ,
16 ga would be ok too ,

solder wire to taillight bulb holder and use a nylon tie within about 10 mm... for strain relief .
the vibration , wiggle and wire-weight
are limited to the... span... between solder and stain relief .

Last edited by quinten; 10/12/20 3:07 pm.
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Dibnah Offline OP
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Thanks quinten, that looks flexible. Could probably run as a spiral coil from the rear mudguard to the tail light for added flexibility.

Another option could be to use a flexible multi-core cable and secure the outer sheath to the tailight. Currently, the cables are flexing as the tail light moves around on the bobbin mounts. I wonder how much it moves around!

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hope it helps .

Quote
Plenty of slack cable adjacent to the fracture points, although the lengh is reducing as I chop bits off!

its counterintuitive but
you could try reducing the slack near the failing solder joint ... to the smaller-est " natural" Bend radius of the wire ... and add
some strain relief , like nylon ties
sometimes its the weight of the wire in a big loop that adds the strain to the solder point .

another possible solution is to add a solid piece of wire as a supportive Armature , not a conductor ,
Alongside of the wire harness and tape/tie the harness to the bigger wire as support .

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Lucas connectors offer no real strain relief, crimped or soldered.
Typical Japanese connectors feature two crimps, one for wire, one for insulation near the connection. That is real strain relief. Bonus: a proper crimping tool is reasonably priced.


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Originally Posted by quentin
you could try reducing the slack near the failing solder joint ... to the smaller-est " natural" Bend radius of the wire ... and add
some strain relief , like nylon tie

Yes, tie the wire near to the joint, so all the flexing is done by a length of plain wire, not the piece gripped in the joint.

It also sounds like you may have more movement than necessary in your anti vibration light mounting.


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Hi David,
Originally Posted by DavidP
Lucas connectors offer no real strain relief, crimped or soldered.
confused

Original Lucas bullet terminals looked like this:-

[Linked Image from autosparks.co.uk]

... they were crimped at the two reduced diameters, one on the conductor strands, the other on the insulation. Having used them for over forty years, I'm not sure I understand "offer no real strain relief"?

Originally Posted by DavidP
Typical Japanese connectors feature two crimps, one for wire, one for insulation near the connection. That is real strain relief. Bonus: a proper crimping tool is reasonably priced.
Ime:-

[Linked Image from autosparks.co.uk]

[Linked Image from autosparks.co.uk]

... original Lucas 1/4" spade terminals looked like these:-

[Linked Image from autosparks.co.uk]

[Linked Image from autosparks.co.uk]

... differences in "strain relief"? They're all crimped by exactly the same reasonably-priced proper crimping tool.

Btw, while they aren't retailed outside GB, @Dibnah can buy bullets that have exactly the same crimp and strain relief as the "Japanese connectors" and the spade terminals but the bullets are 3/16" OD nominal to fit the same snap connectors as the original Lucas bullet terminals.

Hth.

Regards,

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Dibnah Offline OP
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Thanks again for the replies.

There is probably 1/4" lateral movement and 1/4" fore/aft movement for the taillight without too much effort by hand. There is a lot of rotational movement available, which I can't easily measure. I don't think the light unit noticeably moves when revving the engine when stationary, but I've not particularly checked.

Flexible silicone cables as per quinten's link are the first option if the current repairs don't solve the problem. Approx 1000 miles between fractures does suggest that this is a marginal problem i.e. upgrading the cables might be an easy fix.

Cable socks could be a solution for larger cables, but I've not seen anything suitable for smaller cables e.g. 16SWG

( For the avoidance of doubt re: the quality of my soldering smile the soldered joints are ok, the fractures occur adjacent to the soldered joint. )

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