Small rewiring project

[Member 10617]

I want to replace my brakelight switch and the short lengths of electrical wire leading to it. The wiring chart indicates that one strand of wire is Green with Purple and the other should be Green. I know where I can purchase this wire, but what I cannot determine is what size of wire is required: 9 or 14 strands.

Can someone help me with this? Thanks.

 

[DrEntropy]

More "strands" will be less prone to work-hardening failure but the real issue is gauge. #12 is the usual choice for the LBC's IIRC.

HERE'S a helpful little site on the subject.

 

[Member 10617]

Dr. Entrophy,


I see on a chart on British Wiring's homepage that 12 gauge US is equal to British 44 strand wire. the British wiring company rates its wire by strands, so to follow your advice, I should purchase 44 strand Green and Green/Purple wire. They have 44 strand Green, but the highest they go with Green and Purple is 28 strand.

Considering that this is for the very short connection of wire between the connector and the switch, and the Triumph chart calls for Green and Green/Purple, can I get along with using Green for both sides?

28 strands has the carrying capacity of 17.50 amps and is for horns, headlamps, and major accessory feed, while 44 strands carrying capacity is 25.50 amps, for generator, control box, and ammeter. I would think that 28 strands would be sufficient for the brakelight switch.

 

[Geo Hahn]

12ga sounds kinda big (to me) for those wires. Without looking I would have guessed 16ga or so for that part of the harness.

 

[DNK]

Not 12 Gauge ,way top big for that. A lot of normal wiring in the 6 was 28 strand

 

[Geo Hahn]

...Considering that this is for the very short connection of wire between the connector and the switch, and the Triumph chart calls for Green and Green/Purple, can I get along with using Green for both sides?...

Ed -- my English teacher would say 'you can, but you may not'.

Years ago I bought a used (TR4) harness to harvest correct color wire as needed. I can send you a length of green/purple if you want to do it right.

 

[DNK]

I might have what you need.
How long?

 

[Member 10617]

Don and George,

The length to be spanned is very short: about 18 inches. But there are two wires called for in the chart. One is Green (#17 on the wiring chart), and the other is Green and Purple (#22 on the wiring chart).

I thought I'd buy a small supply from British Wiring, but I don't know either the number of strands (British) or the gauge (US) to order. I thought that 14 strand (18 gauge US) might do as it carries 8.00 amps. and is for side and tail lamps and general wiring, or perhaps 28 strand (14 gauge US) as it carries 17.50 Amps. and is for horns & headlamps, major accessory feed. The suggestion that I should use 12 gauge US (44 strand wire) came as a surprise to me.

 

[mrv8q]

Maybe a purple Magic Marker might come in handy to draw a stripe on your green wire.

 

[TR3driver]

Relax, Ed. 28 strand will do just fine (original was probably 14 strand).

Personally, I wouldn't even bother with using proper British wire ... just pick up some green 14 or 16 AWG at the corner FLAPS and be done with it. The electrons don't know what color the insulation is, and no one else is likely to get their head down there to check whether the purple stripe is in place or not.

 

[TR3driver]

Ed -- my English teacher would say 'you can, but you may not'.

But I would say 'you can, and you may'. Meaning that it is both possible and you have my permission.

 

[Geo Hahn]

I can send you 20" lengths of green & green/purple in the same gauge used originally. It is not heavy wire, could be 18ga.

PM me an address if oyu want it.

 

[Member 10617]

Not knowing much about the wiring of these cars, I figured there must be some reason for the different color wires -- different gauges or something like that. Odd thing is that the manuals devote much space to all these color variations, but say nothing about the gauge of wire to use. Seems to me they should give that information so, as you say, we can just go down to the local auto store and get the right wire.

Thank you very much for the offers. George, I'll take you up on your kind offer and will send you a PM.

 

[Member 10617]

Don. Thank you, also, for the kind offer. I'll have plenty with what George has offered to send me.

Randall. You've hit the nail on the head. The color on the wiring insulation doesn't concern me at all. I just want to make sure I use the appropriate "strand" or gauge for this little job.

What did I say... "Little Job." I should have learned by now that there are no "little jobs" with these cars. Chances are I will have trouble getting the old brakelight switch out because it is obviously the original switch. And, as you know, it is in a hard-to-reach place. I once had a '47 Desoto in Tucson that had a brakelight switch that was frozen in place. Mechanics couldn't budge it! I had to install a switch on the dash that I flipped on whenever I stepped on the brake to turn the brake lights on. Hope I won't have to repeat that nonsense.

 

[TR3driver]

Odd thing is that the manuals devote much space to all these color variations, but say nothing about the gauge of wire to use. Seems to me they should give that information so, as you say, we can just go down to the local auto store and get the right wire.

The manuals are written from the point of view that you have a complete car and just need to maintain it. For the longer runs of wire through the harness, the color coding can be very helpful in troubleshooting.

Although I have to say that my original wiring is mostly faded to a uniform brown, and I get by just fine with a diagram, a test light, and a little cogitation.

 

[TR3driver]

Nah, the original switch will come out easy. Although if memory serves, it's easier to get to by going through the wheel well, rather than down from the top. ISTR I used a small (like 8") pair of slip-joint pliers.

And if it won't, there are always alternatives :laugh:

 

[Andrew Mace]

Not knowing much about the wiring of these cars, I figured there must be some reason for the different color wires...

As Randall notes, it's primarily for ease of tracing circuits through the entire car. In this particular case, the main GREEN indicates switched (and fused -- thanks, Randall!) power to a unit such as the brake light switch, and the GREEN w/PURPLE indicates wire to the brake lamp(s).

Here's a useful <span style="font-style: italic">Wiring Colour Code Table</span> from Chris Kantarjiev.

 

[TR3driver]

In this particular case, the main GREEN indicates switched power

Switched and fused. If it was switched but not fused, it would be white. (Eg, the wire to the coil.)

Fused but not switched would be purple, but the only circuit like that on the TR3 is dedicated to the horns (and is brown/green).

 

[DrEntropy]

Sorry for the confusion, Ed. The others are right, #12 would be overkill. #14 or #16 would be fine. And as long as it goes from the solid green, thru the switch to the G/P one at the harness the leads may as well be the same color. I'd do as Randall suggests and just go to the local hardware, autoparts or Radio Shack store and get a short spool of green #14 and be done with it.

ISTR seeing LBC brake switches with <span style="font-style: italic">both</span> leads as solid green at some point, too (but I misled previously with the #12 wire, sooo...).

 

[Member 10617]

Back this morning...

All of this information, as usual, is very helpful, and I thank all of your most warmly.

I assumed that the various color variations were mainly for tracing the wires throuout the car. I was hoping that the color code also revealed something about the gauge of the wire to use, but that, apparently, is not the case.

The manuals are surprisingly silent on what gauge should be used for different applications. Even a manual like Martin Thaddeus' Classic Car Electrics doesn't mention gauge or strands. The only source that comes close is British Wiring's (excellent)homepage that gives the following information:

Cable size in "strands":
Cable size 9 carrying capacity is 5.75 amps
for side and tail lamps & general wiring


Cable size 14 " is 8.00 amps
for same as above



Cable size 28 " is 17.50 amps
for horns & headlamps & major accessory feed

Cable size 44 " is 25.50 amps
for generator, control box, & ammeter

British 14 strand wire = 18 gauge US
British 28 strand wire = 14 gauge US
British 44 strand wire = 12 gauge US
British 65 strand wire = 10 gauge US

Randall, As I surveyed the task, I could see that it would be very difficult to get at the switch from above unless I disconnected parts of my carburetor, so I assumed I would have to come in from below. But the placement of the switch and the location of the frame seemd to spell trouble. I hadn't even thought of going through the wheel well (an obvious choice!).

My only other question has to do with removing the switch itself. I am hoping, of course, that it is not frozen in place. Perhaps because there is so much oil and grease around it, it has been somewhat protected from corrosion. And, I assume that if it come out, brake fluid will follow it unless I quickly plug the hole or insert the new switch. I imagine that the pressure of the brake fluid on the switch creates the contact that lights the brake light.